TI UART使用指南

KeyStone Architecture

Universal Asynchronous Receiver/Transmitter (UART)
User Guide
Literature Number: SPRUGP1
November 2010www.ti.com
Release History
Release Date Chapter/Topic Description/Comments
1.0 November 2010 All Initial Release
?-ii KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
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Contents
Release History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-ii
List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-v
List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-vi
Preface ?-vii
About This Manual. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-vii
Notational Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-vii
Related Documentation from Texas Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-viii
Trademarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?-viii
Chapter 1
Introduction 1-1
1.1 Purpose of the Peripheral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
1.2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
1.3 Functional Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
1.4 Industry Standard(s) Compliance Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Chapter 2
Architecture 2-1
2.1 Clock Generation and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
2.2 Signal Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.3 Pin Multiplexing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.4 Protocol Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.4.1 Transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.4.2 Reception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.4.3 Data Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
2.5 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
2.5.1 Transmission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
2.5.2 Reception. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6
2.5.3 FIFO Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
2.5.3.1 FIFO Interrupt Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7
2.5.3.2 FIFO Poll Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
2.5.4 Autoflow Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
2.5.4.1 UARTn_RTS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
2.5.4.2 UARTn_CTS Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-10
2.5.5 Loopback Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-10
2.6 Reset Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-11
2.6.1 Software Reset Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-11
2.6.2 Hardware Reset Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-11
2.7 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-11
2.8 Interrupt Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-12
2.8.1 Interrupt Events and Requests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-12
2.8.2 Interrupt Multiplexing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-13
2.9 DMA Event Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-13
2.10 Power Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-13
2.11 Emulation Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-14
2.12 Exception Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-14
2.12.1 Divisor Latch Not Programmed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-14
2.12.2 Changing Operating Mode During Busy Serial Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-14
SPRUGP1—November 2010 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide ?-iii
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Chapter 3
Registers 3-1
3.1 Receiver Buffer Register (RBR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
3.2 Transmitter Holding Register (THR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
3.3 Interrupt Enable Register (IER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
3.4 Interrupt Identification Register (IIR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
3.5 FIFO Control Register (FCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
3.6 Line Control Register (LCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-10
3.7 Modem Control Register (MCR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-12
3.8 Line Status Register (LSR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-13
3.9 Modem Status Register (MSR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-16
3.10 Scratch Pad Register (SCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-17
3.11 Divisor Latches (DLL and DLH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-18
3.12 Revision Identification Registers (REVID1 and REVID2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-20
3.13 Power and Emulation Management Register (PWREMU_MGMT). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-21
3.14 Mode Definition Register (MDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-22
Index IX-1
?-iv KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
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List of Tables
Table 2-1 Baud Rate Examples for 150-MHz UART Input Clock and 16× Oversampling Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Table 2-2 Baud Rate Examples for 150-MHz UART Input Clock and 13× Oversampling Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Table 2-3 UART Signal Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Table 2-4 Character Time for Word Lengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8
Table 2-5 UART Interrupt Requests Descriptions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12
Table 3-1 UART Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Table 3-2 Receiver Buffer Register (RBR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Table 3-3 Transmitter Holding Register (THR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Table 3-4 Interrupt Enable Register (IER) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Table 3-5 Interrupt Identification Register (IIR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Table 3-6 Interrupt Identification and Interrupt Clearing Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
Table 3-7 FIFO Control Register (FCR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Table 3-8 Line Control Register (LCR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Table 3-9 Relationship Between ST, EPS, and PEN Bits in LCR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Table 3-10 Number of STOP Bits Generated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
Table 3-11 Modem Control Register (MCR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
Table 3-12 Line Status Register (LSR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Table 3-13 Modem Status Register (MSR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
Table 3-14 Scratch Pad Register (MSR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
Table 3-15 Divisor LSB Latch (DLL) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18
Table 3-16 Divisor MSB Latch (DLH) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19
Table 3-17 Revision Identification Register 1 (REVID1) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Table 3-18 Revision Identification Register 2 (REVID2) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Table 3-19 Power and Emulation Management Register (PWREMU_MGMT) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21
Table 3-20 Mode Definition Register (MDR) Field Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22
SPRUGP1—November 2010 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide ?-v
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List of Figures
Figure 1-1 KeyStone Device Universal Asynchronous Receiver/Transmitter (UART) Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
Figure 2-1 UART Clock Generation Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
Figure 2-2 Relationships Between Data Bit, BCLK, and UART Input Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Figure 2-3 UART Protocol Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5
Figure 2-4 UART Interface Using Autoflow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
Figure 2-5 Autoflow Functional Timing Waveforms for UARTn_RTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9
Figure 2-6 Autoflow Functional Timing Waveforms for UARTn_CTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
Figure 2-7 UART Interrupt Request Enable Paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
Figure 3-1 Receiver Buffer Register (RBR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Figure 3-2 Transmitter Holding Register (THR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Figure 3-3 Interrupt Enable Register (IER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5
Figure 3-4 Interrupt Identification Register (IIR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
Figure 3-5 FIFO Control Register (FCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8
Figure 3-6 Line Control Register (LCR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10
Figure 3-7 Modem Control Register (MCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12
Figure 3-8 Line Status Register (LSR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13
Figure 3-9 Modem Status Register (MSR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16
Figure 3-10 Scratch Pad Register (SCR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17
Figure 3-11 Divisor LSB Latch (DLL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18
Figure 3-12 Divisor MSB Latch (DLH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19
Figure 3-13 Revision Identification Register 1 (REVID1). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Figure 3-14 Revision Identification Register 2 (REVID2). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-20
Figure 3-15 Power and Emulation Management Register (PWREMU_MGMT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21
Figure 3-16 Mode Definition Register (MDR). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-22
?-vi KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
Submit Documentation Feedback Preface
About This Manual
The Universal Asynchronous Receiver/Transmitter (UART) performs
serial-to-parallel conversions on data received from a peripheral device and
parallel-to-serial conversion on data received from the CPU. The UART includes
control capability and a processor interrupt system that can be tailored to minimize
software management of the communications link.
Notational Conventions
This document uses the following conventions:
? Commands and keywords are in boldface font.
? Arguments for which you supply values are in italic font.
? Terminal sessions and information the system displays are in screen font.
? Information you must enter is in boldface screen font.
? Elements in square brackets ([ ]) are optional.
Notes use the following conventions:
Note—Means reader take note. Notes contain helpful suggestions or references
to material not covered in the publication.
The information in a caution or a warning is provided for your protection. Please read
each caution and warning carefully.
CAUTION—Indicates the possibility of service interruption if precautions are
not taken.
WARNING—Indicates the possibility of damage to equipment if precautions are
not taken.
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Related Documentation from Texas Instruments
Enhanced Direct Memory Access 3 (EDMA3) for KeyStone Devices User Guide SPRUGS5
Packet Accelerator (PA) for KeyStone Devices User Guide SPRUGS4
Power Sleep Controller (PSC) for KeyStone Devices User Guide SPRUGV4
Trademarks
TMS320C66x and C66x are trademarks of Texas Instruments Incorporated.
All other brand names and trademarks mentioned in this document are the property of Texas Instruments
Incorporated or their respective owners, as applicable.
?-viii KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
Submit Documentation Feedback Chapter 1
Introduction
The following sections provide an overview of the main components and features of the
Universal Asynchronous Receiver/Transmitter (UART) peripheral.
1. 1 "Purpose of the Peripheral" on page 1-2
1. 2 "Features" on page 1-2
1. 3 "Functional Block Diagram" on page 1-3
1. 4 "Industry Standard(s) Compliance Statement " on page 1-4
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1.1 Purpose of the Peripheral
The Universal Asynchronous Receiver/Transmitter (UART) peripheral is based on the
industry standard TL16C550 asynchronous communications element, which in turn is
a functional upgrade of the TL16C450. Functionally similar to the TL16C450 on power
up (single character or TL16C450 mode), the UART can be placed in an alternate FIFO
(TL16C550) mode. This relieves the CPU of excessive software overhead by buffering
received and transmitted characters. The receiver and transmitter FIFOs store up to 16
bytes including three additional bits of error status per byte for the receiver FIFO.
The UART performs serial-to-parallel conversions on data received from a peripheral
device and parallel-to-serial conversion on data received from the CPU. The CPU can
read the UART status at any time. The UART includes control capability and a
processor interrupt system that can be tailored to minimize software management of
the communications link.
The UART includes a programmable baud generator capable of dividing the UART
input clock by divisors from 1 to 65535 and producing a 16× reference clock or a 13×
reference clock for the internal transmitter and receiver logic. For detailed timing and
electrical specifications for the UART, see the device-specific data manual.
1.2 Features
Check the device-specific data manual to see the list of features that are supported and
that are not supported by the UART.
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1.3 Functional Block Diagram
A functional block diagram of the UART is shown in Figure 1-1.
Figure 1-1 KeyStone Device Universal Asynchronous Receiver/Transmitter (UART) Block Diagram
S
e
8 8
l
Receiver
e
FIFO
8
c
t
Receiver
UARTn_RXD
Peripheral
8
Shift
Bus Data Receiver
Register pin
Bus Buffer
Buffer Register
16
Receiver
Line
Timing and
Control
Control
Register
Divisor
Latch (LS)
16 Baud
Generator
Divisor
Latch (MS)
Transmitter
Line
Timing and
Status
Control
Register
8 Transmitter 8
S
FIFO
e
l
e Transmitter
Transmitter
8 8 UARTn_TXD
c Shift
Holding
pin
t Register
Register
Modem
8 Control
Control
Logic
Register
Interrupt Interrupt/
8
Enable Event
Interrupt to CPU
Register Control
Logic
Event to DMA controller
Interrupt
8
Identification
Power and
Register
Emulation
Control
FIFO Register
Control
Register
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1.4 Industry Standard(s) Compliance Statement
The UART peripheral is based on the industry standard TL16C550 asynchronous
communications element, which is a functional upgrade of the TL16C450. The
information in this document assumes familiarity with these standards.
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Submit Documentation Feedback Chapter 2
Architecture
The following sections give an overview of the main components and features of the
Universal Asynchronous Receiver/Transmitter (UART).
2. 1 "Clock Generation and Control" on page 2-2
2. 2 "Signal Descriptions" on page 2-4
2. 3 "Pin Multiplexing" on page 2-4
2. 4 "Protocol Description" on page 2-4
2. 5 "Operation" on page 2-6
2. 6 "Reset Considerations" on page 2-11
2. 7 "Initialization" on page 2-11
2. 8 "Interrupt Support" on page 2-12
2. 9 "DMA Event Support" on page 2-13
2.1 0 "Power Management" on page 2-13
2.1 1 "Emulation Considerations " on page 2-14
2.1 2 "Exception Processing" on page 2-14
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2.1 Clock Generation and Control
The UART bit clock is derived from an input clock to the UART. See the device-specific
manual to check the maximum data rate supported by the UART.
Figure 2-1 is a conceptual clock generation diagram for the UART. The processor clock
generator receives a signal from an external clock source and produces a UART input
clock with a programmed frequency. The UART contains a programmable baud
generator that takes an input clock and divides it by a divisor in the range between 1
16
and (2 - 1) to produce a baud clock (BCLK). The frequency of BCLK is sixteen times
(16×) the baud rate (each received or transmitted bit lasts 16 BCLK cycles) or thirteen
times (13×) the baud rate (each received or transmitted bit lasts 13 BCLK cycles). When
th
the UART is receiving, the bit is sampled in the 8 BCLK cycle for 16× over sampling
th
mode and on the 6 BCLK cycle for 13× oversampling mode.
Figure 2-1 UART Clock Generation Diagram
Processor
UART
Receiver
DLH:DLL Timingand
Control
UART InputClock BCLK
Clock
Baud
InputClock
Generator
Generator
Transmitter
Timingand
Control
OtherLogic
The 16× or 13× reference clock is selected by configuring the OSM_SEL bit in the mode
definition register (MDR). The formula to calculate the divisor is:
UART Input Clock Frequency
[MDR.OSM_SEL = 0]
Divisor =
Desired Baud Rate × 16
UART Input Clock Frequency
[MDR.OSM_SEL = 1]
Divisor =
Desired Baud Rate × 13
Two 8-bit register fields (DLH and DLL), called divisor latches, hold this 16-bit divisor.
DLH holds the most significant bits of the divisor, and DLL holds the least significant
bits of the divisor. For information about these register fields, see Section 3.11. These
divisor latches must be loaded during initialization of the UART to ensure desired
operation of the baud generator. Writing to the divisor latches results in two wait states
being inserted during the write access while the baud generator is loaded with the new
value.
Figure 2-2 summarizes the relationship between the transferred data bit, BCLK, and
the UART input clock. Note that the timing relationship in Figure 2-2 shows that each
bit lasts for 16 BCLK cycles. This is in case of 16× oversampling mode. For 13×
oversampling mode each bit lasts for 13 BCLK cycles.
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Figure 2-2 Relationships Between Data Bit, BCLK, and UART Input Clock
nUART inputclockcycles,where n =divisor inDLH:DLL
UART inputclock
n
BCLK
Eachbit lasts16BCLKcycles.
Whenreceiving,theUARTsamplesthebit inthe8th cycle.
BCLK
UARTn_TXD,
D1 D2
UARTn_RXD
D0
UARTn_TXD,
START PARITY STOP1 STOP2
D0 D1 D2 D3 D4 D5 D6 D7
UARTn_RXD
Example baud rates and divisor values relative to a 150-MHz UART input clock and
16× oversampling mode are shown in Table 2-1.
Table 2-1 Baud Rate Examples for 150-MHz UART Input Clock and 16× Oversampling Mode
Baud Rate Divisor Value Actual Baud Rate Error (%)
2400 3906 2400.154 0.01
4800 1953 4800.372 0.01
9600 977 9595.701 –0.04
19200 488 19211.066 0.06
38400 244 38422.131 0.06
56000 167 56137.725 0.25
128000 73 129807.7 0.33
3000000 3 3125000 4.00
Example baud rates and divisor values relative to a 150-MHz UART input clock and
16× oversampling mode are shown in Table 2-2.
Table 2-2 Baud Rate Examples for 150-MHz UART Input Clock and 13× Oversampling Mode
Baud Rate Divisor Value Actual Baud Rate Error (%)
2400 4808 2399 –0.01
4800 2404 4799.646 –0.01
9600 1202 9599.386 –0.01
19200 601 19198.771 –0.01
38400 300 38461.538 0.16
56000 206 56011.949 0.02
128000 90 128205.128 0.16
3000000 4 2884615.385 –4.00
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2.2 Signal Descriptions
UARTs use a minimal number of signal connections to interface with external devices.
The UART signal descriptions are included in Table 2-3. Note that the number of
UARTs and their supported features vary on each device, see the device-specific data
manual for more details.
Table 2-3 UART Signal Descriptions
1
Signal Name Signal Type Function
UARTn_TXD Output Serial data transmit
UARTn_RXD Input Serial data receive
2
UARTn_CTS Input Clear-to-Send handshaking signal
2
UARTn_RTS Output Request-to-Send handshaking signal
1. The value n indicates the applicable UART; that is, UART0, UART1, etc.
2. This signal is not supported in all UARTs. See the device-specific data manual to check if it is supported.
2.3 Pin Multiplexing
Extensive pin multiplexing is used to accommodate the largest number of peripheral
functions in the smallest possible package. Pin multiplexing is controlled using a
combination of hardware configuration at device reset and software programmable
register settings. See the device-specific data manual to determine how pin
multiplexing affects the UART.
2.4 Protocol Description
2.4.1 Transmission
The UART transmitter section includes a transmitter hold register (THR) and a
transmitter shift register (TSR). When the UART is in the FIFO mode, THR is a 16-byte
FIFO. Transmitter section control is a function of the UART line control register
(LCR). Based on the settings chosen in the LCR, the UART transmitter sends the
following to the receiving device:
?1 S T A R T b i t
? 5, 6, 7, or 8 data bits
? 1 PARITY bit (optional)
? 1, 1.5, or 2 STOP bits
2.4.2 Reception
The UART receiver section includes a receiver shift register (RSR) and a receiver buffer
register (RBR). When the UART is in the FIFO mode, RBR is a 16-byte FIFO. Receiver
section control is a function of the UART line control register (LCR). Based on the
settings chosen in LCR, the UART receiver accepts the following from the transmitting
device:
?1 S T A R T b i t
? 5, 6, 7, or 8 data bits
? 1 PARITY bit (optional)
? 1 STOP bit (any other STOP bits transferred with the above data are not detected)
2.4.3 Data Format
The UART transmits in the following format:
1 START bit + data bits (5, 6, 7, 8) + 1 PARITY bit (optional) + STOP bit (1, 1.5, 2)
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It transmits 1 START bit; 5, 6, 7, or 8 data bits, depending on the data width selection;
1 PARITY bit, if parity is selected; and 1, 1.5, or 2 STOP bits, depending on the STOP
bit selection.
The UART receives in the following format:
1 START bit + data bits (5, 6, 7, 8) + 1 PARITY bit (optional) + 1 STOP bit
It receives 1 START bit; 5, 6, 7, or 8 data bits, depending on the data width selection; 1
PARITY bit, if parity is selected; and 1 STOP bit.
The protocol formats are shown in Figure 2-3.
Figure 2-3 UART Protocol Formats
Transmit/Receive for5-bit data, parity Enable, 1 STOP bit
D0 D3
D1 D2 D4 PARITY STOP1
Transmit/Receive for 6-bit data, parity Enable, 1 STOP bit
D0 D1 D2 D3 D4 D5 PARITY STOP1
Transmit/Receive for7-bit data, parity Enable, 1 STOP bit
D0 D1 D2 D3 D4 D5 D6 PARITY STOP1
Transmit/Receive for 8-bit data, parity Enable, 1 STOP bit
D0 D1 D2 D3 D4 D5 D6 D7 PARITY STOP1
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2.5 Operation
2.5.1 Transmission
The UART transmitter section includes a transmitter hold register (THR) and a
transmitter shift register (TSR). When the UART is in the FIFO mode, THR is a 16-byte
FIFO. Transmitter section control is a function of the UART line control register
(LCR). Based on the settings chosen in LCR, the UART transmitter sends the following
to the receiving device:
1. 1 START bit
2. 5, 6, 7, or 8 data bits
3. 1 PARITY bit (optional)
4. 1, 1.5, or 2 STOP bits
THR receives data from the internal data bus, and when TSR is ready, the UART moves
the data from THR to TSR. The UART serializes the data in TSR and transmits the data
on the UARTn_TXD pin. In the non-FIFO mode, if THR is empty and the THR empty
interrupt is enabled in the interrupt enable register (IER), an interrupt is generated.
This interrupt is cleared when a character is loaded into THR. In the FIFO mode, the
interrupt is generated when the transmitter FIFO is empty, and it is cleared when at
least one byte is loaded into the FIFO.
2.5.2 Reception
The UART receiver section includes a receiver shift register (RSR) and a receiver buffer
register (RBR). When the UART is in the FIFO mode, RBR is a 16-byte FIFO. Timing
is supplied by the 16T receiver clock. Receiver section control is a function of the UART
line control register (LCR). Based on the settings chosen in LCR, the UART receiver
accepts the following from the transmitting device:
?1 S T A R T b i t
? 5, 6, 7, or 8 data bits
? 1 PARITY bit (optional)
? 1 STOP bit (any other STOP bits transferred with the above data are not detected)
RSR receives the data bits from the UARTn_RXD pin. Then RSR concatenates the data
bits and moves the resulting value into RBR (or the receiver FIFO). The UART also
stores three bits of error status information next to each received character, to record a
parity error, framing error, or break.
In the non-FIFO mode, when a character is placed in RBR and the receiver data-ready
interrupt is enabled in the interrupt enable register (IER), an interrupt is generated.
This interrupt is cleared when the character is read from RBR. In the FIFO mode, the
interrupt is generated when the FIFO is filled to the trigger level selected in the FIFO
control register (FCR), and it is cleared when the FIFO contents drop below the trigger
level.
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2.5.3 FIFO Modes
The following two modes can be used for servicing the receiver and transmitter FIFOs:
? FIFO interrupt mode. The FIFO is enabled and the associated interrupts are
enabled. Interrupts are sent to the CPU to indicate when specific events occur.
? FIFO poll mode. The FIFO is enabled but the associated interrupts are disabled.
The CPU polls status bits to detect specific events.
Because the receiver FIFO and the transmitter FIFO are controlled separately, either
one or both can be placed into the interrupt mode or the poll mode.
2.5.3.1 FIFO Interrupt Mode
When the receiver FIFO is enabled in the FIFO control register (FCR) and the receiver
interrupts are enabled in the interrupt enable register (IER), the interrupt mode is
selected for the receiver FIFO. The following are important points about the receiver
interrupts:
? The receiver data-ready interrupt is issued to the CPU when the FIFO has
reached the trigger level that is programmed in FCR. It is cleared when the CPU
or the DMA controller reads enough characters from the FIFO such that the
FIFO drops below its programmed trigger level.
? The receiver line status interrupt is generated in response to an overrun error, a
parity error, a framing error, or a break. This interrupt has higher priority than
the receiver data-ready interrupt. For details, see Section 2.8 ‘‘Interrupt
Support’’.
? The data-ready (DR) bit in the line status register (LSR) indicates the presence or
absence of characters in the receiver FIFO. The DR bit is set when a character is
transferred from the receiver shift register (RSR) to the empty receiver FIFO. The
DR bit remains set until the FIFO is empty again.
? A receiver time-out interrupt occurs if all of the following conditions exist:
– At least one character is in the FIFO,
– The most recent character was received more than four continuous character
times ago. A character time is the time allotted for 1 START bit, n data bits,
1 PARITY bit, and 1 STOP bit, where n depends on the word length selected
with the WLS bits in the line control register (LCR). See Table 2-4.
– The most recent read of the FIFO has occurred more than four continuous
character times before.
? Character times are calculated by using the baud rate.
? When a receiver time-out interrupt has occurred, it is cleared and the time-out
timer is cleared when the CPU or the EDMA controller reads one character from
the receiver FIFO. The interrupt is also cleared if a new character is received in
the FIFO or if the URRST bit is cleared in the power and emulation management
register (PWREMU_MGMT).
? If a receiver time-out interrupt has not occurred, the time-out timer is cleared
after a new character is received or after the CPU or EDMA reads the receiver
FIFO.
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When the transmitter FIFO is enabled in FCR and the transmitter holding register
empty interrupt is enabled in IER, the interrupt mode is selected for the transmitter
FIFO. The transmitter holding register empty interrupt occurs when the
transmitter FIFO is empty. It is cleared when the transmitter hold register (THR) is
loaded (1 to 16 characters may be written to the transmitter FIFO while servicing this
interrupt).
Table 2-4 Character Time for Word Lengths
Word Length (n) Character Time Four Character Times
5 Time for 8 bits Time for 32 bits
6 Time for 9 bits Time for 36 bits
7 Time for 10 bits Time for 40 bits
8 Time for 11 bits Time for 44 bits
2.5.3.2 FIFO Poll Mode
When the receiver FIFO is enabled in the FIFO control register (FCR) and the receiver
interrupts are disabled in the interrupt enable register (IER), the poll mode is selected
for the receiver FIFO. Similarly, when the transmitter FIFO is enabled and the
transmitter interrupts are disabled, the transmitted FIFO is in the poll mode. In the poll
mode, the CPU detects events by checking bits in the line status register (LSR):
? The RXFIFOE bit indicates whether there are any errors in the receiver FIFO.
? The TEMT bit indicates that both the transmitter holding register (THR) and the
transmitter shift register (TSR) are empty.
? The THRE bit indicates when THR is empty.
? The BI (break), FE (framing error), PE (parity error), and OE (overrun error) bits
specify which error or errors have occurred.
? The DR (data-ready) bit is set as long as there is at least one byte in the receiver
FIFO.
Also, in the FIFO poll mode:
? The interrupt identification register (IIR) is not affected by any events because
the interrupts are disabled.
? The UART does not indicate when the receiver FIFO trigger level is reached or
when a receiver time-out occurs.
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2.5.4 Autoflow Control
The UART can employ autoflow control by connecting the UARTn_CTS and
UARTn_RTS signals. Note that all UARTs do not support autoflow control, see the
device-specific data manual for supported features. The UARTn_CTS input must be
active before the transmitter FIFO can transmit data. The UARTn_RTS becomes active
when the receiver needs more data and notifies the sending device. When UARTn_RTS
is connected to UARTn_CTS, data transmission does not occur unless the receiver
FIFO has space for the data. Therefore, when two UARTs are connected as shown in
Figure 2-4 with autoflow enabled, overrun errors are eliminated.
Figure 2-4 UART Interface Using Autoflow Diagram
UART UART
UARTn_RXD
Serialto tx Para Parall lleellto to
Parallel Ser Seriiaall
Receiver Transmitter
FIFO FIFO
UARTn_RTS
Flow cts Fl Flow ow
Control Contro Controll
D[7:0]
D[7:0]
UARTn_TXD
Parallelto Ser Seriiaallto to
rx
Serial Para Parall lleell
Transmitter Receiver
FIFO FIFO
UARTn_CTS
Flow rts Fl Flow ow
Control Contro Controll
DSP Off-chip
2.5.4.1 UARTn_RTS Behavior
UARTn_RTS data flow control originates in the receiver block (Figure 1-1 on
page 1-3). When the receiver FIFO level reaches a trigger level of 1, 4, 8, or 14 (see
Figure 2-5), UARTn_RTS is deasserted. The sending UART may send an additional
byte after the trigger level is reached (assuming the sending UART has another byte to
send), because it may not recognize the deassertion of UARTn_RTS until after it has
begun sending the additional byte. For trigger level 1, 4, and 8, UARTn_RTS is
automatically reasserted after the receiver FIFO is emptied. For trigger level 14,
UARTn_RTS is automatically reasserted when the receiver FIFO drops below the
trigger level.
Figure 2-5 Autoflow Functional Timing Waveforms for UARTn_RTS
Start Start Stop Stop Start Stop Start
Bits N
Bits N+1
UARTn_RXD
UARTn_RTS
(A) The N = Receiver FIFI trigger level.
(B) The two blocks in dashed lines cover the case in which an additional byte is sent.
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2.5.4.2 UARTn_CTS Behavior
The transmitter checks UARTn_CTS before sending the next data byte. If
UARTn_CTS is active, the transmitter sends the next byte. To stop the transmitter
from sending the following byte, UARTn_CTS must be released before the middle of
the last STOP bit that is currently being sent (see Figure 2-6). When flow control is
enabled, UARTn_CTS level changes do not trigger interrupts because the device
automatically controls its own transmitter. Without autoflow control, the transmitter
sends any data present in the transmitter FIFO and a receiver overrun error may result.
Figure 2-6 Autoflow Functional Timing Waveforms for UARTn_CTS
Start Bits0?7 Start Bits 0?7 Start Bits 0?7
UARTn_TXD Stop Stop Stop
UARTn_CTS
(A) When UARTn_CTS is active (low), the transmitter keeps sending serial data out.
(B) When UARTn_CTS goes high before the middle of the last STOP bit of the current byte, the transmitter finishes sending the current byte but it does not send the next byte.
(C) When UARTn_CTS goes from high to low, the transmitter begins sending data again.
2.5.5 Loopback Control
The UART can be placed in the diagnostic mode using the LOOP bit in the modem
control register (MCR), which internally connects the UART output back to the UART
input. In this mode, the transmit and receive data paths, the transmitter and receiver
interrupts, and the modem control interrupts can be verified without connecting to
another UART.
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2.6 Reset Considerations
2.6.1 Software Reset Considerations
Two bits in the power and emulation management register (PWREMU_MGMT)
control resetting the parts of the UART:
? The UTRST bit controls resetting the transmitter only. If UTRST = 1, the
transmitter is active; if UTRST = 0, the transmitter is in reset.
? The URRST bit controls resetting the receiver only. If URRST = 1, the receiver is
active; if URRST = 0, the receiver is in reset.
In each case, putting the receiver and/or transmitter in reset will reset the state machine
of the affected portion but does not affect the UART registers.
2.6.2 Hardware Reset Considerations
When the processor RESET pin is asserted, the entire processor is reset and is held in
the reset state until the RESET pin is released. As part of a device reset, the UART state
machine is reset and the UART registers are forced to their default states. The default
states of the registers are shown in Chapter 3 ‘‘Registers’’ on page 3-1.
2.7 Initialization
The following steps are required to initialize the UART:
1. Perform the necessary device pin multiplexing setup (see the device-specific data
manual).
2. Set the desired baud rate by writing the appropriate clock divisor values to the
divisor latch registers (DLL and DLH).
3. If the FIFOs will be used, select the desired trigger level and enable the FIFOs by
writing the appropriate values to the FIFO control register (FCR). The FIFOEN
bit in FCR must be set first, before the other bits in FCR are configured.
4. Choose the desired protocol settings by writing the appropriate values to the line
control register (LCR).
5. If autoflow control is desired, write appropriate values to the modem control
register (MCR). Note that all UARTs do not support autoflow control, see the
device-specific data manual for supported features.
6. Choose the desired response to emulation suspend events by configuring the
FREE bit and enable the UART by setting the UTRST and URRST bits in the
power and emulation management register (PWREMU_MGMT).
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2.8 Interrupt Support
2.8.1 Interrupt Events and Requests
The UART generates the interrupt requests described in Table 2-5. All requests are
multiplexed through an arbiter to a single UART interrupt request to the CPU, as
shown in Figure 2-7. Each of the interrupt requests has an enable bit in the interrupt
enable register (IER) and is recorded in the interrupt identification register (IIR).
If an interrupt occurs and the corresponding enable bit is set to 1, the interrupt request
is recorded in IIR and is forwarded to the CPU. If an interrupt occurs and the
corresponding enable bit is cleared to 0, the interrupt request is blocked. The interrupt
request is neither recorded in IIR nor forwarded to the CPU.
Table 2-5 UART Interrupt Requests Descriptions
UART Interrupt Request Interrupt Source Comment
THREINT THR-empty condition: The transmitter holding register If THREINT is enabled in IER, by setting the ETBEI bit, it is
(THR) or the transmitter FIFO is empty. All of the data has recorded in IIR.
been copied from THR to the transmitter shift register
As an alternative to using THREINT, the CPU can poll the THRE
(TSR).
bit in the line status register (LSR).
RDAINT Receive data available in non-FIFO mode or trigger level If RDAINT is enabled in IER, by setting the ERBI bit, it is
reached in the FIFO mode. recorded in IIR.
As an alternative to using RDAINT, the CPU can poll the DR bit
in the line status register (LSR). In the FIFO mode, this is not
a functionally equivalent alternative because the DR bit
does not respond to the FIFO trigger level. The DR bit
indicates only the presence or absence of unread
characters.
RTOINT Receiver time-out condition (in the FIFO mode only): The receiver time-out interrupt prevents the UART from
No characters have been removed from or input to the waiting indefinitely when the receiver FIFO level is below
receiver FIFO during the last four character times (see the trigger level and, therefore, does not generate a
Table 2-4), and there is at least one character in the receiver data-ready interrupt.
receiver FIFO during this time.
If RTOINT is enabled in IER, by setting the ERBI bit, it is
recorded in IIR.
There is no status bit to reflect the occurrence of a time-out
condition.
RLSINT Receiver line status condition: An overrun error, parity ? If RLSINT is enabled in IER, by setting the ELSI bit, it is
error, framing error, or break has occurred. recorded in IIR.
? As an alternative to using RLSINT, the CPU can poll the
following bits in the line status register (LSR): overrun error
indicator (OE), parity error indicator (PE), framing error
indicator (FE), and break indicator (BI).
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Figure 2-7 UART Interrupt Request Enable Paths
Conditions Enable bits UART Interrupt Requests
Transmitter Holding
Register Empty THREINT
IER(ETBEI)
ReceiverDataReady
RDRINT
IER(ERBI)
UART Interrupt
Arbiter
RTOINT
RequesttoCPU
ReceiverTime-out
Overrun Error
RLSINT
ParityError
IER(ELSI)
Framing Error
Break
2.8.2 Interrupt Multiplexing
The UARTs have dedicated interrupt signals to the CPU and the interrupts are not
multiplexed with any other interrupt source.
2.9 DMA Event Support
In the FIFO mode, the UART generates the following two DMA events:
? Receive event (URXEVT): The trigger level for the receiver FIFO (1, 4, 8, or 14
characters) is set with the RXFIFTL bit in the FIFO control register (FCR). Every
time the trigger level is reached or a receiver time-out occurs, the UART sends a
receive event to the EDMA controller. In response, the EDMA controller reads
the data from the receiver FIFO by way of the receiver buffer register (RBR).
? Transmit event (UTXEVT): When the transmitter FIFO is empty (when the last
byte in the transmitter FIFO has been copied to the transmitter shift register), the
UART sends an UTXEVT signal to the EDMA controller. In response, the
EDMA controller refills the transmitter FIFO by way of the transmitter holding
register (THR). The UTXEVT signal is also sent to the DMA controller when the
UART is taken out of reset using the UTRST bit in the power and emulation
management register (PWREMU_MGMT).
Activity in DMA channels can be synchronized to these events. In the non-FIFO mode,
the UART generates no DMA events. Any DMA channel synchronized to either of
these events must be enabled at the time the UART event is generated. Otherwise, the
DMA channel will miss the event and, unless the UART generates a new event, no data
transfer will occur.
2.10 Power Management
The UART peripheral can be placed in reduced-power modes to conserve power
during periods of low activity. The power management of the UART peripheral is
controlled by the processor Power and Sleep Controller (PSC). The PSC acts as a master
controller for power management for all of the peripherals on the device. For detailed
information on power management procedures using the PSC, see the Power Sleep
Controller (PSC) for KeyStone Devices User Guide in ‘‘Related Documentation from
Texas Instruments’’ on page ?-viii.
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2.11 Emulation Considerations
The FREE bit in the power and emulation management register (PWREMU_MGMT)
determines how the UART responds to an emulation suspend event such as an
emulator halt or breakpoint. If FREE = 0 and a transmission is in progress, the UART
halts after completing the one-word transmission; if FREE = 0 and a transmission is not
in progress, the UART halts immediately. If FREE = 1, the UART does not halt and
continues operating normally.
Note also that emulator accesses are essentially transparent to UART operation.
Emulator read operations do not affect any register contents, status bits, or operating
states. Emulator writes, however, may affect register contents and may affect UART
operation, depending on what register is accessed and what value is written.
The UART registers can be read from or written to during emulation suspend events,
even if the UART activity has stopped.
2.12 Exception Processing
2.12.1 Divisor Latch Not Programmed
Since the processor reset signal has no effect on the divisor latch, the divisor latch will
have an unknown value after power up. If the divisor latch is not programmed after
power up, the baud clock (BCLK) will not operate and will instead be set to a constant
logic 1 state.
The divisor latch values should always be reinitialized following a processor reset.
2.12.2 Changing Operating Mode During Busy Serial Communication
Since the serial link characteristics are based on how the control registers are
programmed, the UART will expect the control registers to be static while it is busy
engaging in a serial communication. Therefore, changing the control registers while the
module is still busy communicating with another serial device will most likely cause an
error condition and should be avoided.
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3. 1 "Receiver Buffer Register (RBR)" on page 3-3
3. 2 "Transmitter Holding Register (THR)" on page 3-4
3. 3 "Interrupt Enable Register (IER)" on page 3-5
3. 4 "Interrupt Identification Register (IIR)" on page 3-6
3. 5 "FIFO Control Register (FCR) " on page 3-8
3. 6 "Line Control Register (LCR)" on page 3-10
3. 7 "Modem Control Register (MCR)" on page 3-12
3. 8 "Line Status Register (LSR)" on page 3-13
3. 9 "Modem Status Register (MSR)" on page 3-16
3.1 0 "Scratch Pad Register (SCR)" on page 3-17
3.1 1 "Divisor Latches (DLL and DLH) " on page 3-18
3.1 2 "Revision Identification Registers (REVID1 and REVID2)" on page 3-20
3.1 3 "Power and Emulation Management Register (PWREMU_MGMT)" on page 3-21
3.1 4 "Mode Definition Register (MDR)" on page 3-22
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The system programmer has access to and control over any of the UART registers that
are listed in Table 3-1. These registers, which control UART operations, receive data,
and transmit data, are available at 32-bit addresses in the device memory map. See the
device-specific data manual for the memory address of these registers.
? RBR, THR, and DLL share one address. When the DLAB bit in LCR is 0, reading
from the address gives the content of RBR, and writing to the address modifies
THR. When DLAB = 1, all accesses at the address read or modify DLL. DLL can
also be accessed with address offset 20h.
? IER and DLH share one address. When DLAB = 0, all accesses read or modify
IER. When DLAB = 1, all accesses read or modify DLH. DLH can also be accessed
with address offset 24h.
? IIR and FCR share one address. Regardless of the value of the DLAB bit, reading
from the address gives the content of IIR, and writing modifies FCR.
Table 3-1 UART Registers
Offset Acronym Register Description Section
0h RBR Receiver Buffer Register (read only) Section 3.1
0h THR Transmitter Holding Register (write only) Section 3.2
4h IER Interrupt Enable Register Section 3.3
8h IIR Interrupt Identification Register (read only) Section 3.4
8h FCR FIFO Control Register (write only) Section 3.5
Ch LCR Line Control Register Section 3.6
10h MCR Modem Control Register Section 3.7
14h LSR Line Status Register Section 3.8
18h MSR Modem Status Register Section 3.9
1Ch SCR Scratch Pad Register Section 3.10
20h DLL Divisor LSB Latch Section 3.11
24h DLH Divisor MSB Latch Section 3.11
28h REVID1 Revision Identification Register 1 Section 3.12
2Ch REVID2 Revision Identification Register 2 Section 3.12
30h PWREMU_MGMT Power and Emulation Management Register Section 3.13
34h MDR Mode Definition Register Section 3.14
End of Table 3-1
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3.1 Receiver Buffer Register (RBR)
The UART receiver section consists of a receiver shift register (RSR) and a receiver
buffer register (RBR). When the UART is in the FIFO mode, RBR is a 16-byte FIFO.
Timing is supplied by the 16× receiver clock or 13× receiver clock by programming
OSM_SEL bit field of MDR register. Receiver section control is a function of the line
control register (LCR).
The RSR receives serial data from the UARTn_RXD pin. Then the RSR concatenates
the data and moves it into the RBR (or the receiver FIFO). In the non-FIFO mode,
when a character is placed in RBR and the receiver data-ready interrupt is enabled
(DR = 1 in the IER), an interrupt is generated. This interrupt is cleared when the
character is read from the RBR. In the FIFO mode, the interrupt is generated when the
FIFO is filled to the trigger level selected in the FIFO control register (FCR), and it is
cleared when the FIFO contents drop below the trigger level.
Access considerations:
? The RBR, THR, and DLL share one address. To read the RBR, write 0 to the
DLAB bit in the LCR, and read from the shared address. When DLAB = 0, writing
to the shared address modifies thee THR. When DLAB = 1, all accesses at the
shared address read or modify the DLL.
? The DLL also has a dedicated address. If the dedicated address is used, DLAB
can = 0, so that the RBR and THR are always selected at the shared address.
The RBR is shown in Figure 3-1 and described in Table 3-2.
Figure 3-1 Receiver Buffer Register (RBR)
31 16
Reserved
R-0
15 8 7 0
Reserved DATA
R-0 R-0
Legend: R = Read only; W = Write only; -n = value after reset
Table 3-2 Receiver Buffer Register (RBR) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7-0 DATA 0-FFh Received data.
End of Table 3-2
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3.2 Transmitter Holding Register (THR)
The UART transmitter section consists of a transmitter hold register (THR) and a
transmitter shift register (TSR). Transmitter control is a function of the line control
register (LCR).
The THR receives data from the internal data bus. When the TSR is idle the UART then
moves the data from the THR to the TSR. The UART serializes the data in the TSR and
transmits the data on the TX pin.
In the non-FIFO mode, if the THR is empty and the TSR is empty, the THRE interrupt
is enabled (ETBEI = 1 in the IER), and an interrupt is generated. This interrupt is
cleared when a character is loaded into the THR.
When the UART is in the FIFO mode, the THR is a 16-byte FIFO. In the FIFO mode,
the interrupt is generated when the transmitter FIFO is empty, and it is cleared when
at least one byte is loaded into the FIFO.
Access considerations:
? The RBR, THR, and DLL share one address. To load the THR, write 0 to the
DLAB bit of the LCR, and write to the shared address. When DLAB = 0, reading
from the shared address gives the content of the RBR. When DLAB = 1, all
accesses at the address read or modify the DLL.
? The DLL also has a dedicated address. If the dedicated address is used, DLAB
can = 0, so that the RBR and the THR are always selected at the shared address.
The transmitter holding register (THR) is shown in Figure 3-2 and described in
Table 3-3.
Figure 3-2 Transmitter Holding Register (THR)
31 16
Reserved
R-0
15 8 7 0
Reserved DATA
R-0 R-0
Legend: R = Read only; W = Write only; -n = value after reset
Table 3-3 Transmitter Holding Register (THR) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7-0 DATA 0-FFh Data to transmit.
End of Table 3-3
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3.3 Interrupt Enable Register (IER)
The interrupt enable register (IER) is used to individually enable or disable each type
of interrupt request that can be generated by the UART. Each interrupt request that is
enabled in the IER is forwarded to the CPU.
Access considerations:
? The IER and DLH share one address. To read or modify the IER, write 0 to the
DLAB bit in the LCR. When DLAB = 1, all accesses at the shared address read or
modify the DLH.
? The DLH also has a dedicated address. If the dedicated address is used, DLAB
can = 0, so that the IER is always selected at the shared address.
The IER is shown in Figure 3-3 and described in Table 3-4.
Figure 3-3 Interrupt Enable Register (IER)
31 16
Reserved
R-0
15 43 0
Reserved EDSSI ELSI ETBEI ERBI
R-0 R/W-0 R/W-0 R/W-0 R/W-0
Legend: R = Read only; R/W = Read/Write; -n = value after reset
Table 3-4 Interrupt Enable Register (IER) Field Descriptions
Bit Field Value Description
31-4 Reserved 0 Reserved
3 EDSSI 0 Enable modem status interrupt.
2 ELSI Receiver line status interrupt enable.
0 = Receiver line status interrupt is disabled.
1 = Receiver line status interrupt is enabled.
1 ETBEI Transmitter holding register empty interrupt enable.
0 = Transmitter holding register empty interrupt is disabled.
1 = Transmitter holding register empty interrupt is enabled.
0 ERBI Receiver data available interrupt and character timeout indication interrupt enable.
0 = Receiver data available interrupt and character timeout indication interrupt is disabled.
1 = Receiver data available interrupt and character timeout indication interrupt is enabled.
End of Table 3-4
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3.4 Interrupt Identification Register (IIR)
The interrupt identification register (IIR) is a read-only register at the same address as
the FIFO control register (FCR), which is a write-only register. When an interrupt is
generated and enabled in the interrupt enable register (IER), the IIR indicates that an
interrupt is pending in the IPEND bit and encodes the type of interrupt in the INTID
bits.
The UART has an on-chip interrupt generation and prioritization capability that
permits flexible communication with the CPU. The UART provides three priority
levels of interrupts:
? Priority 1 - Receiver line status (highest priority)
? Priority 2 - Receiver data ready or receiver timeout
? Priority 3 - Transmitter holding register empty
The FIFOEN bit in the IIR can be checked to determine whether the UART is in the
FIFO mode or the non-FIFO mode.
Access consideration:
The IIR and FCR share one address. Regardless of the value of the DLAB bit in the LCR,
reading from the address gives the content of the IIR, and writing to the address
modifies the FCR.
The IIR is shown in Figure 3-4 and described in Table 3-5.
Figure 3-4 Interrupt Identification Register (IIR)
31 16
Reserved
R-0
15 876543 10
Reserved FIFOEN Reserved INTID IPEND
R-0 R-0 R-0 R-0 R-1
Legend: R = Read only; -n = value after reset
Table 3-5 Interrupt Identification Register (IIR) Field Descriptions (Part 1 of 2)
Bit Field Value Description
31-8 Reserved 0 Reserved
7-6 FIFOEN 0-3h FIFOs enabled.
0 = Non-FIFO mode.
1 = Reserved.
2 = Reserved.
3 = FIFOs are enabled. FIFOEN bit in the FIFO control register (FCR) is set to 1.
5-4 Reserved 0 Reserved
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Table 3-5 Interrupt Identification Register (IIR) Field Descriptions (Part 2 of 2)
Bit Field Value Description
3-1 INTID 0-7h Interrupt type. See Table 3-6.
0 = Reserved.
1 = Transmitter holding register empty (priority 3).
2 = Receiver data available (priority 2).
3 = Receiver line status (priority 1, highest).
4 = Reserved.
5 = Reserved.
6 = Character timeout indication (priority 2).
7 = Reserved.
0 IPEND Interrupt pending.
When any UART interrupt is generated and is enabled in IER, IPEND is forced to 0. IPEND remains 0 until all
pending interrupts are cleared or until a hardware reset occurs. If no interrupts are enabled, IPEND is never
forced to 0.
0 = Interrupts pending.
1 = No interrupts pending.
End of Table 3-5
Table 3-6 Interrupt Identification and Interrupt Clearing Information
IIR Bits
Priority
Level 3 2 1 0 Interrupt Type Interrupt Source Event That Clears Interrupt
None 0001None None None
1 0 1 1 0 Receiver line status Overrun error, parity error, framing error, or For an overrun error, reading the line status register
break is detected. (LSR) clears the interrupt. For a parity error, framing
error, or break, the interrupt is cleared only after all
the erroneous data have been read.
2 0 1 0 0 Receiver data-ready Non-FIFO mode: Receiver data is ready. Non-FIFO mode: The receiver buffer register (RBR) is
read.
1
FIFO mode: Trigger level reached. If four FIFO mode: The FIFO drops below the trigger level.
character times (see Table 2-4) pass with no
access of the FIFO, the interrupt is asserted
again.
2 1 1 0 0 Receiver time-out FIFO mode only: No characters have been One of the following events:
removed from or input to the receiver FIFO 1
? A character is read from the receiver FIFO.
during the last four character times (see
? A new character arrives in the receiver FIFO.
Table 2-4), and there is at least one character in
? The URRST bit in the power and emulation
the receiver FIFO during this time.
management register (PWREMU_MGMT) is
loaded with 0.
3 0 0 1 0 Transmitter holding ? Non-FIFO mode: Transmitter holding register A character is written to the transmitter holding
register empty (THR) is empty. register (THR).
? FIFO mode: Transmitter FIFO is empty.
End of Table 3-6
1. In the FIFO mode, the receiver data-ready interrupt or receiver time-out interrupt is cleared by the CPU or by the DMA controller, whichever reads from the receiver FIFO
first.
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3.5 FIFO Control Register (FCR)
The FIFO control register (FCR) is a write-only register at the same address as the
interrupt identification register (IIR), which is a read-only register. Use the FCR to
enable and clear the FIFOs and to select the receiver FIFO trigger level. The FIFOEN
bit must be set to 1 before other FCR bits are written to or the FCR bits are not
programmed.
Access consideration:
The IIR and FCR share one address. Regardless of the value of the DLAB bit, reading
from the address gives the content of the IIR, and writing to the address modifies the
FCR.
CAUTION—For proper communication between the UART and the EDMA
controller, the DMAMODE1 bit must be set to 1. Always write a 1 to the
DMAMODE1 bit, and after a hardware reset, change the DMAMODE1 bit
from 0 to 1.
The FCR is shown in Figure 3-5 and described in Table 3-7
Figure 3-5 FIFO Control Register (FCR)
31 16
Reserved
R-0
15 87654 3 210
1
Reserved RXFIFTL Reserved DMAMODE1 TXCLR RXCLR FIFOEN
R-0 R-0 R-0 W-0 W1C-0 W1C-0 W-0
Legend: R = Read only; W = Write only; W1C = Write 1 to clear (writing 0 has no effect); -n = value after reset
1. Always write 1 to the DMAMODE1 bit. After a hardware reset, change the DMAMODE1 bit from 0 to 1. DMAMODE = 1 is required for proper communication between the
UART and the DMA controller.
Table 3-7 FIFO Control Register (FCR) Field Descriptions (Part 1 of 2)
Bit Field Value Description
31-8 Reserved 0 Reserved
7-6 RXFIFTL 0-3h Receiver FIFO trigger level. RXFIFTL sets the trigger level for the receiver FIFO. When the trigger level is
reached, a receiver data-ready interrupt is generated (if the interrupt request is enabled). When the FIFO
drops below the trigger level, the interrupt is cleared.
0 = 1 byte.
1 = 4 bytes.
2 = 8 bytes.
3 = 14 bytes.
5-4 Reserved 0 Reserved
3 DMAMODE1 DMA MODE1 enable if FIFOs are enabled. Always write 1 to DMAMODE1. After a hardware reset,
change DMAMODE1 from 0 to 1. DMAMOD1 = 1 is a requirement for proper communication between the
UART and the EDMA controller.
0 = DMA MODE1 is disabled.
1 = DMA MODE1 is enabled.
2 TXCLR Transmitter FIFO clear. Write a 1 to TXCLR to clear the bit.
0 = No effect.
1 = Clears transmitter FIFO and resets the transmitter FIFO counter. The shift register is not cleared.
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Table 3-7 FIFO Control Register (FCR) Field Descriptions (Part 2 of 2)
Bit Field Value Description
1 RXCLR Receiver FIFO clear. Write a 1 to RXCLR to clear the bit.
0 = No effect.
1 = Clears receiver FIFO and resets the receiver FIFO counter. The shift register is not cleared.
0 FIFOEN Transmitter and receiver FIFOs mode enable. FIFOEN must be set before other FCR bits are written to or the
FCR bits are not programmed. Clearing this bit clears the FIFO counters.
0 = Non-FIFO mode. The transmitter and receiver FIFOs are disabled, and the FIFO pointers are cleared.
1 = FIFO mode. The transmitter and receiver FIFOs are enabled.
End of Table 3-7
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3.6 Line Control Register (LCR)
The system programmer controls the format of the asynchronous data communication
exchange by using the line control register (LCR). In addition, the programmer can
retrieve, inspect, and modify the content of the LCR. This eliminates the need for
separate storage of the line characteristics in system memory.
The LCR is shown in Figure 3-6 and described in Table 3-8.
Figure 3-6 Line Control Register (LCR)
31 16
Reserved
R-0
15 876543210
Reserved DLAB BC SP EPS PEN STB WLS
R-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
Legend: R = Read only; R/W = Read/Write; -n = value after reset
Table 3-8 Line Control Register (LCR) Field Descriptions (Part 1 of 2)
Bit Field Value Description
31-8 Reserved 0 Reserved.
7 DLAB Divisor latch access bit. The divisor latch registers (DLL and DLH) can be accessed at dedicated addresses or at
addresses shared by RBR, THR, and IER. Using the shared addresses requires toggling DLAB to change which
registers are selected. If the dedicated addresses are used, DLAB can = 0.
0 = Allows access to the receiver buffer register (RBR), the transmitter holding register (THR), and the interrupt
enable register (IER) selected. At the address shared by RBR, THR, and DLL, the CPU can read from RBR and
write to THR. At the address shared by IER and DLH, the CPU can read from and write to IER.
1 = Allows access to the divisor latches of the baud generator during a read or write operation (DLL and DLH).
At the address shared by RBR, THR, and DLL, the CPU can read from and write to DLL. At the address shared
by IER and DLH, the CPU can read from and write to DLH.
6 BC Break control.
0 = Break condition is disabled.
1 = Break condition is transmitted to the receiving UART. A break condition is a condition in which the
UARTn_TXD signal is forced to the spacing (cleared) state.
5 SP Stick parity. The SP bit works in conjunction with the EPS and PEN bits. The relationship between the SP, EPS,
and PEN bits is summarized in Table 3-9.
0 = Stick parity is disabled.
1 = Stick parity is enabled.
? When odd parity is selected (EPS = 0), the PARITY bit is transmitted and checked as set.
? When even parity is selected (EPS = 1), the PARITY bit is transmitted and checked as cleared.
4 EPS Even parity select. Selects the parity when parity is enabled (PEN = 1). The EPS bit works in conjunction with
the SP and PEN bits. The relationship between the SP, EPS, and PEN bits is summarized in Table 3-9.
0 = Odd parity is selected (an odd number of logic 1s is transmitted or checked in the data and PARITY bits).
1 = Even parity is selected (an even number of logic 1s is transmitted or checked in the data and PARITY bits).
3 PEN Parity enable. The PEN bit works in conjunction with the SP and EPS bits. The relationship between the SP, EPS,
and PEN bits is summarized in Table 3-9.
0 = No PARITY bit is transmitted or checked.
1 = Parity bit is generated in transmitted data and is checked in received data between the last data word bit
and the first STOP bit.
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Table 3-8 Line Control Register (LCR) Field Descriptions (Part 2 of 2)
Bit Field Value Description
2 STB Number of STOP bits generated. STB specifies 1, 1.5, or 2 STOP bits in each transmitted character. When STB =
1, the WLS bit determines the number of STOP bits. The receiver clocks only the first STOP bit, regardless of the
number of STOP bits selected. The number of STOP bits generated is summarized in Table 3-10.
0 = One STOP bit is generated.
1 = WLS bit determines the number of STOP bits:
? When WLS = 0, 1.5 STOP bits are generated.
? When WLS = 1h, 2h, or 3h, 2 STOP bits are generated.
1-0 WLS 0-3h Word length select. Number of bits in each transmitted or received serial character. When STB = 1, the WLS bit
determines the number of STOP bits.
0 = 5 bits
1 = 6 bits
2 = 7 bits
3 = 8 bits
End of Table 3-8
Table 3-9 Relationship Between ST, EPS, and PEN Bits in LCR
ST Bit EPS Bit PEN Bit Parity Option
x x 0 Parity disabled: No PARITY bit is transmitted or checked.
0 0 1 Odd parity selected: Odd number of logic 1s.
0 1 1 Even parity selected: Even number of logic 1s.
1 0 1 Stick parity selected with PARITY bit transmitted and checked as set.
1 1 1 Stick parity selected with PARITY bit transmitted and checked as cleared.
End of Table 3-9
Table 3-10 Number of STOP Bits Generated
ST Bit WLS Bit Word Length Selected with WLS Bits Number of STOP Bits Generated Baud Clock (BCLK) Cycles
0x A n y w o r d l e n g t h 1 1 6
10 h 5 b i t s 1 . 5 2 4
11 h 6 b i t s 2 3 2
12 h 7 b i t s 2 3 2
13 h 8 b i t s 2 3 2
End of Table 3-10
SPRUGP1—November 2010 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide 3-11
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3.7 Modem Control Register (MCR)
The modem control register (MCR) provides the ability to enable/disable the autoflow
functions, and enable/disable the loopback function for diagnostic purposes.
The MCR is shown in Figure 3-7 and described in Table 3-11.
Figure 3-7 Modem Control Register (MCR)
31 16
Reserved
R-0
15 6543210
1 1
Reserved AFE LOOP OUT2 OUT1 RTS Reserved
R-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R-0
Legend: R = Read only; R/W = Read/Write; -n = value after reset
1. All UARTs do not support this feature. See the device-specific data manual for supported features. If this feature is not available, this bit is reserved and should be cleared
to 0.
Table 3-11 Modem Control Register (MCR) Field Descriptions
Bit Field Value Description
31-6 Reserved 0 Reserved
5 AFE Autoflow control enable. Autoflow control allows the UARTn_RTS and UARTn_CTS signals to provide
handshaking between UARTs during data transfer. When AFE = 1, the RTS bit determines the autoflow control
enabled. Note that all UARTs do not support this feature. See the device-specific data manual for supported
features. If this feature is not available, this bit is reserved and should be cleared to 0.
0 = Autoflow control is disabled.
1 = Autoflow control is enabled:
? When RTS = 0, only UARTn_CTS is enabled.
? When RTS = 1, UARTn_RTS and UARTn_CTS are enabled.
4 LOOP Loopback mode enable. LOOP is used for the diagnostic testing using the loopback feature.
0 = Loopback mode is disabled.
1 = Loopback mode is enabled. When LOOP is set, the following occur:
? The UARTn_TXD signal is set high.
? The UARTn_RXD pin is disconnected
? The output of the transmitter shift register (TSR) is looped back in to the receiver shift register (RSR) input.
3O U T 2 0 O U T 2 C o n t r o l B i t .
2O U T 1 0 O U T 1 C o n t r o l B i t .
1 RTS RTS control. When AFE = 1, the RTS bit determines the autoflow control enabled. Note that all UARTs do not
support this feature. See the device-specific data manual for supported features. If this feature is not available,
this bit is reserved and should be cleared to 0.
0 = UARTn_RTS is disabled, only UARTn_CTS is enabled.
1 = UARTn_RTS and UARTn_CTS are enabled.
0 Reserved 0 Reserved
End of Table 3-11
3-12 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
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3.8 Line Status Register (LSR)
The line status register (LSR) provides information to the CPU concerning the status
of data transfers. It is intended for read operations only — do not write to this register.
Bits 1 through 4 record the error conditions that produce a receiver line status
interrupt.
The LSR is shown in Figure 3-8 and described in Table 3-12.
Figure 3-8 Line Status Register (LSR)
31 16
Reserved
R-0
15 876543210
Reserved RXFIFOE TEMT THRE BIS FE PE OE DR
R-0 R-0 R-1 R-1 R-0 R-0 R-0 R-0 R-0
Legend: R = Read only; -n = value after reset
Table 3-12 Line Status Register (LSR) Field Descriptions (Part 1 of 3)
Bit Field Value Description
31-8 Reserved 0 Reserved
7 RXFIFOE Receiver FIFO error.
In non-FIFO mode:
0 = There has been no error, or RXFIFOE was cleared because the CPU read the erroneous character from the
receiver buffer register (RBR).
1 = There is a parity error, framing error, or break indicator in the receiver buffer register (RBR).
In FIFO mode:
0 = There has been no error, or RXFIFOE was cleared because the CPU read the erroneous character from the
receiver FIFO and there are no more errors in the receiver FIFO.
1 = At least one parity error, framing error, or break indicator in the receiver FIFO.
6 TEMT Transmitter empty (TEMT) indicator.
In non-FIFO mode:
0 = Either the transmitter holding register (THR) or the transmitter shift register (TSR) contains a data character.
1 = Both the transmitter holding register (THR) and the transmitter shift register (TSR) are empty.
In FIFO mode:
0 = Either the transmitter FIFO or the transmitter shift register (TSR) contains a data character.
1 = Both the transmitter FIFO and the transmitter shift register (TSR) are empty.
5 THRE Transmitter holding register empty (THRE) indicator. If the THRE bit is set and the corresponding interrupt enable
bit is set (ETBEI = 1 in IER), an interrupt request is generated.
In non-FIFO mode:
0 = Transmitter holding register (THR) is not empty. THR has been loaded by the CPU.
1 = Transmitter holding register (THR) is empty (ready to accept a new character). The content of THR has been
transferred to the transmitter shift register (TSR).
In FIFO mode:
0 = Transmitter FIFO is not empty. At least one character has been written to the transmitter FIFO. The transmitter
FIFO may be written to if it is not full.
1 = Transmitter FIFO is empty. The last character in the FIFO has been transferred to the transmitter shift register
(TSR).
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Table 3-12 Line Status Register (LSR) Field Descriptions (Part 2 of 3)
Bit Field Value Description
4 BI Break indicator. The BI bit is set whenever the receive data input (UARTn_RXD) was held low for longer than a
full-word transmission time. A full-word transmission time is defined as the total time to transmit the START, data,
PARITY, and STOP bits. If the BI bit is set and the corresponding interrupt enable bit is set (ELSI = 1 in IER), an
interrupt request is generated.
In non-FIFO mode:
0 = No break has been detected, or the BI bit was cleared because the CPU read the erroneous character from the
receiver buffer register (RBR).
1 = A break has been detected with the character in the receiver buffer register (RBR).
In FIFO mode:
0 = No break has been detected, or the BI bit was cleared because the CPU read the erroneous character from the
receiver FIFO and the next character to be read from the FIFO has no break indicator.
1 = A break has been detected with the character at the top of the receiver FIFO.
3 FE Framing error (FE) indicator. A framing error occurs when the received character does not have a valid STOP bit. In
response to a framing error, the UART sets the FE bit and waits until the signal on the RX pin goes high. When the
RX signal goes high, the receiver is ready to detect a new START bit and receive new data. If the FE bit is set and the
corresponding interrupt enable bit is set (ELSI = 1 in IER), an interrupt request is generated.
In non-FIFO mode:
0 = No framing error has been detected, or the FE bit was cleared because the CPU read the erroneous data from
the receiver buffer register (RBR).
1 = A framing error has been detected with the character in the receiver buffer register (RBR).
In FIFO mode:
0 = No framing error has been detected, or the FE bit was cleared because the CPU read the erroneous data from
the receiver FIFO and the next character to be read from the FIFO has no framing error.
1 = A framing error has been detected with the character at the top of the receiver FIFO.
2 PE Parity error (PE) indicator. A parity error occurs when the parity of the received character does not match the parity
selected with the EPS bit in the line control register (LCR). If the PE bit is set and the corresponding interrupt enable
bit is set (ELSI = 1 in IER), an interrupt request is generated.
In non-FIFO mode:
0 = No parity error has been detected, or the PE bit was cleared because the CPU read the erroneous data from
the receiver buffer register (RBR).
1 = A parity error has been detected with the character in the receiver buffer register (RBR).
In FIFO mode:
0 = No parity error has been detected, or the PE bit was cleared because the CPU read the erroneous data from
the receiver FIFO and the next character to be read from the FIFO has no parity error.
1 = A parity error has been detected with the character at the top of the receiver FIFO.
1 OE Overrun error (OE) indicator. An overrun error in the non-FIFO mode is different from an overrun error in the FIFO
mode. If the OE bit is set and the corresponding interrupt enable bit is set (ELSI = 1 in IER), an interrupt request is
generated.
In non-FIFO mode:
0 = No overrun error has been detected, or the OE bit was cleared because the CPU read the content of the line
status register (LSR).
1 Overrun error has been detected. Before the character in the receiver buffer register (RBR) could be read, it was
overwritten by the next character arriving in RBR.
In FIFO mode:
0 = No overrun error has been detected, or the OE bit was cleared because the CPU read the content of the line
status register (LSR).
1 = Overrun error has been detected. If data continues to fill the FIFO beyond the trigger level, an overrun error
occurs only after the FIFO is full and the next character has been completely received in the shift register. An
overrun error is indicated to the CPU as soon as it happens. The new character overwrites the character in the
shift register, but it is not transferred to the FIFO.
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Table 3-12 Line Status Register (LSR) Field Descriptions (Part 3 of 3)
Bit Field Value Description
0 DR Data-ready (DR) indicator for the receiver. If the DR bit is set and the corresponding interrupt enable bit is set
(ERBI = 1 in IER), an interrupt request is generated.
In non-FIFO mode:
0 = Data is not ready, or the DR bit was cleared because the character was read from the receiver buffer register
(RBR).
1 = Data is ready. A complete incoming character has been received and transferred into the receiver buffer
register (RBR).
In FIFO mode:
0 = Data is not ready, or the DR bit was cleared because all of the characters in the receiver FIFO have been read.
1 = Data is ready. There is at least one unread character in the receiver FIFO. If the FIFO is empty, the DR bit is set
as soon as a complete incoming character has been received and transferred into the FIFO. The DR bit remains
set until the FIFO is empty again.
End of Table 3-12
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3.9 Modem Status Register (MSR)
The modem status register (MSR) provides information to the CPU concerning the
status of modem control signals. It is intended for read operations only — do not write
to this register.
The MSR is shown in Figure 3-9 and described in Table 3-13.
Figure 3-9 Modem Status Register (MSR)
31 16
Reserved
R-0
15 876543210
Reserved CD RI DSR CTS DCD TERI DDSR DCTS
R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0 R-0
Legend: R = Read only; -n = value after reset
Table 3-13 Modem Status Register (MSR) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7 CD 0 Complement of the Carrier Detect input. When the UART is in the diagnostic test mode (loopback mode
MCR[4] = 1), this bit is equal to the MCR bit 3 (OUT2).
6 RI 0 Complement of the Ring Indicator input. When the UART is in the diagnostic test mode (loopback mode
MCR[4] = 1), this bit is equal to the MCR bit 2 (OUT1).
5 DSR 0 Complement of the Data Set Ready input. When the UART is in the diagnostic test mode (loopback mode
MCR[4] = 1), this bit is equal to the MCR bit 0 (DTR).
4 CTS 0 Complement of the Clear To Send input. When the UART is in the diagnostic test mode (loopback mode
MCR[4] = 1), this bit is equal to the MCR bit 1 (RTS).
3 DCD 0 Change in DCD indicator bit. DCD indicates that the DCD input has changed state since the last time it was
read by the CPU. When DCD is set and the modem status interrupt is enabled, a modem status interrupt is
generated.
2 TERI 0 Trailing edge of RI (TERI) indicator bit. TERI indicates that the RI input has changed from a low to a high.
When TERI is set and the modem status interrupt is enabled, a modem status interrupt is generated.
1 DDSR 0 Change in DSR indicator bit. DDSR indicates that the DSR input has changed state since the last time it was
read by the CPU. When DDSR is set and the modem status interrupt is enabled, a modem status interrupt is
generated.
0 DCTS 0 Change in CTS indicator bit. DCTS indicates that the CTS input has changed state since the last time it was
read by the CPU. When DCTS is set (autoflow control is not enabled and the modem status interrupt is
enabled), a modem status interrupt is generated. When autoflow control is enabled, no interrupt is
generated.
End of Table 3-13
3-16 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
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3.10 Scratch Pad Register (SCR)
The scratch pad register (SCR) is intended for the programmer''s use as a scratch pad.
It temporarily holds the programmer''s data without affecting UART operation.
The SCR is shown in Figure 3-10 and described in Table 3-14.
Figure 3-10 Scratch Pad Register (SCR)
31 16
Reserved
R-0
15 8 7 0
Reserved SCR
R-0 R-0
Legend: R = Read only; -n = value after reset
Table 3-14 Scratch Pad Register (MSR) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7-0 SCR 0 These bits are intended for the programmer''s use as a scratch pad in the sense that it temporarily holds the
programmer''s data without affecting any other UART operation.
End of Table 3-14
SPRUGP1—November 2010 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide 3-17
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3.11 Divisor Latches (DLL and DLH)
Two 8-bit register fields (DLL and DLH), called divisor latches, store the 16-bit divisor
for generation of the baud clock in the baud generator. The latches are in the DLH and
DLL. The DLH holds the most-significant bits of the divisor, and the DLL holds the
least-significant bits of the divisor. These divisor latches must be loaded during
initialization of the UART to ensure desired operation of the baud generator. Writing
to the divisor latches results in two wait states being inserted during the write access
while the baud generator is loaded with the new value.
Access considerations:
? The RBR, THR, and DLL share one address. When DLAB = 1 in the LCR, all
accesses at the shared address are accesses to the DLL. When DLAB = 0, reading
from the shared address gives the content of the RBR, and writing to the shared
address modifies the THR.
? The IER and DLH share one address. When DLAB = 1 in the LCR, accesses to the
shared address read or modify the DLH. When DLAB = 0, all accesses at the
shared address read or modify the IER.
The DLL and DLH also have dedicated addresses. If dedicated addresses are used, the
DLAB bit can be kept cleared, so that the RBR, THR, and IER are always selected at the
shared addresses.
The divisor LSB latch (DLL) is shown in Figure 3-11 and described in Table 3-15.
Figure 3-11 Divisor LSB Latch (DLL)
31 16
Reserved
R-0
15 8 7 0
Reserved DLL
R-0 R/W-0
Legend: R = Read only; R/W = Read/Write; -n = value after reset
Table 3-15 Divisor LSB Latch (DLL) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7-0 DLL 0-Fh The 8 least-significant bits (LSBs) of the 16-bit divisor for generation of the baud clock in the baud rate
generator.
End of Table 3-15
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The divisor MSB latch (DLH) is shown in Figure 3-12 and described in Table 3-16.
Figure 3-12 Divisor MSB Latch (DLH)
31 16
Reserved
R-0
15 8 7 0
Reserved DLH
R-0 R-0
Legend: R = Read only; -n = value after reset
Table 3-16 Divisor MSB Latch (DLH) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7-0 DLH 0-Fh The 8 most-significant bits (MSBs) of the 16-bit divisor for generation of the baud clock in the baud rate
generator. Maximum baud rate is 128 kbps.
End of Table 3-16
SPRUGP1—November 2010 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide 3-19
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3.12 Revision Identification Registers (REVID1 and REVID2)
Revision identification registers (REVID1 and REVID2) contain peripheral
identification data for the peripheral.
The REVID1 is shown in Figure 3-13 and described in Table 3-17.
Figure 3-13 Revision Identification Register 1 (REVID1)
31 0
REVID1
R-1102 0002h
Legend: R = Read only; -n = value after reset
Table 3-17 Revision Identification Register 1 (REVID1) Field Descriptions
Bit Field Value Description
31-0 REVID1 1102 0002h Peripheral identification number.
End of Table 3-17
The REVID2 is shown in Figure 3-14 and described in Table 3-18.
Figure 3-14 Revision Identification Register 2 (REVID2)
31 16
Reserved
R-0
15 8 7 0
Reserved REVID2
R-0 R-0
Legend: R = Read only; -n = value after reset
Table 3-18 Revision Identification Register 2 (REVID2) Field Descriptions
Bit Field Value Description
31-8 Reserved 0 Reserved
7-0 REVID2 0 Peripheral identification number.
End of Table 3-18
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3.13 Power and Emulation Management Register (PWREMU_MGMT)
The power and emulation management register (PWREMU_MGMT) is shown in
Figure 3-15 and described in Table 3-19.
Figure 3-15 Power and Emulation Management Register (PWREMU_MGMT)
31 16
Reserved
R-0
15 14 13 12 10
Reserved UTRST URRST Reserved FREE
R/W-0 R/W-0 R/W-0 R-1 R/W-0
Legend: R = Read only; R/W = Read/Write; -n = value after reset
Table 3-19 Power and Emulation Management Register (PWREMU_MGMT) Field Descriptions
Bit Field Value Description
31-16 Reserved 0 Reserved
15 Reserved 0 Reserved. This bit must always be written as 0.
14 UTRST UART transmitter reset. Resets and enables the transmitter.
0 = Transmitter is disabled and in reset state.
1 = Transmitter is enabled.
13 URRST UART receiver reset. Resets and enables the receiver.
0 = Receiver is disabled and in reset state.
1 = Receiver is enabled.
12-1 Reserved 1 Reserved
0 FREE Free-running enable mode bit. This bit determines the emulation mode functionality of the UART. When
halted, the UART can handle register read/write requests, but does not generate any
transmission/reception, interrupts or events.
0 = If a transmission is not in progress, the UART halts immediately. If a transmission is in progress, the
UART halts after completion of the one-word transmission.
1 = Free-running mode is enabled. UART continues to run normally.
End of Table 3-19
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3.14 Mode Definition Register (MDR)
The Mode Definition register (MDR) determines the oversampling mode for the
UART. The MDR is shown in Figure 3-16 and described in Table 3-20.
Figure 3-16 Mode Definition Register (MDR)
31 16
Reserved
R-0
15 10
Reserved OSM_SEL
R-0 R/W-0
Legend: R = Read only; R/W = Read/Write; -n = value after reset
Table 3-20 Mode Definition Register (MDR) Field Descriptions
Bit Field Value Description
31-1 Reserved 0 Reserved
0O S M _ S E L O v e r - S a m p l i n g M o d e S e l e c t .
0 = 16× oversampling.
1 = 13× oversampling.
End of Table 3-20
3-22 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
Submit Documentation Feedback Index
map, 3-2
A
module, 2-14
architecture, 2-1
O
B
on-chip, 3-6
buffer, 2-4, 2-6, 2-13, 3-2 to 3-3, 3-7, 3-10, 3-13 to 3-15
output(s), 2-4, 2-10, 3-12
bus(es), 2-6, 3-4
oversampling, 2-2 to 2-3, 3-22
C
P
clock, 1-2, 2-2 to 2-3, 2-6, 2-11, 2-14, 3-3, 3-11, 3-18 to 3-19
package, 2-4
compliance, 1-4
PASS (Packet Accelerator Subsystem), 3-7
configuration, 2-4
peripherals, 2-13
CPU, ?-vii, 1-2, 2-7 to 2-8, 2-12 to 2-13, 3-5 to 3-7, 3-10, 3-13 to 3-14, 3-16
power
management, 2-13
D
PSC (Power and Sleep Controller), ?-viii, 2-13
DMA (Direct Memory Access), 2-7, 2-13, 3-7 to 3-8
R
E
reset, 2-4, 2-11, 2-13 to 2-14, 3-3 to 3-8, 3-10, 3-12 to 3-13, 3-16 to 3-22
EDMA (Enhanced DMA Controller), 2-7, 2-13, 3-8
Rx, 3-14
EFUSE (Electronic Fuse)
power management, 2-13
S
electrical, 1-2
sampling, 2-2, 3-22
EMU (emulation), 2-7, 2-11, 2-13 to 2-14, 3-2, 3-7, 3-21
SCR (Switched Central Resource), 3-2, 3-17
emulation, 2-7, 2-11, 2-13 to 2-14, 3-2, 3-7, 3-21
signal, 2-2, 2-4, 2-13 to 2-14, 3-10, 3-12, 3-14
error reporting and messages, 1-2, 2-3, 2-6 to 2-8, 2-10, 2-12, 2-14, 3-7,
sleep mode, ?-viii, 2-13
3-13 to 3-14
status register, 2-7 to 2-8, 2-12, 3-2, 3-7, 3-13 to 3-14, 3-16
STB (System Trace Buffer), 3-10 to 3-11
I
interface, 2-4, 2-9
T
interrupt, ?-vii, 1-2, 2-6 to 2-8, 2-12 to 2-13, 3-2 to 3-8, 3-10, 3-13 to 3-16
timers, 2-7
trace buffers
L
STB (System Trace Buffer), 3-10 to 3-11
loopback, 2-10, 3-12, 3-16
Tx, 3-4
M
U
memory
UART (Universal Asynchronous Receiver Transmitter), ?-vii, 1-2 to 1-4,
DMA, 2-7, 2-13, 3-7 to 3-8
2-2 to 2-6, 2-8 to 2-14, 3-2 to 3-8, 3-10, 3-14, 3-16 to 3-18, 3-21 to 3-22
general, ?-viii, 3-2, 3-10
SPRUGP1—November 2010 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide IX-1
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IX-2 KeyStone Architecture Universal Asynchronous Receiver/Transmitter (UART) User Guide SPRUGP1—November 2010
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