Content originally posted in LPCWare by Dave on Tue Aug 21 10:31:43 MST 2012
When you blow this up, you see the following sequence:
Write Address 20h => Address of PCA9554 (0x40>>1), <A=Acknowledge>
Command 01h => Command byte WRITE, <A=Acknowledge>
Value 77h =>Value to data to port, <A=Acknowledge>, <P=Stop>
Write Address 26h => Address of PCA9555 (0x4C>>1), <A=Acknowledge>
Command 00h => Command byte INPUT PORT 0 SELECT, <A=Acknowledge>, <P=Stop>
Read Address 26h => Address of PCA9555 (0x4C>>1), <A=Acknowledge>
Lower Byte Value 77h => read lower order byte, auto increment next read to higher order byte, <A=Acknowledge>
Higher Byte Value FFh => read higher order byte, auto decrement next read to lower order byte, <N=No-acknowledge>
NOT SURE WHERE THE 7Fh AND < A > ARE FROM, OR WHY THEY ARE THERE???