IntegratedTechnologyExpress,Inc.
ITTM-AN-99007,July.1Page1of1
ApplicationNoteofIT8761Ffor
PowerOnStrappingCircuit
July1,1999
?Poweronstrappingcircuitneedsextraattentionwhena“0”
settingisselected
Description:DuetoIT8761Rev.Bpoweronstrappingpinsselection,a“0”
settingmaynotbestrappedincorrectly.
Cause:IT8761choosesTXD1andRTS1#pinsforpoweronstrapping
setting,sincethesetwopinalsoconnectto1488/1489typeline
driverandsomeofthelinedriverinternallyhave+12Vpullup
witha11Kohmresistor,thiswillcausethe“0”settingnot
correctlystrapped.
Suggestion:(1)Chooseasmallenoughvaluepulldownresistortomakethe
strappinglinevoltagebelow0.5Vwhensystemisreset.A
suggestedresistorvalueis680ohm.
(2)ImplementaredundantgatebetweenIT8671andlinedriver
toisolatetheinterfereoftheinternalpullupof1488/89line
driverasfollowingcircuit.
4.7K
740712IT87611488/89TXD1/RTS1#
|
|
