Quote Originally Posted by richard View Post
is that the current device or the one that got zapped ?
I found a 8574a in my junk box and fed your code into it (no lcd) and it seems ok (address is $78 for a version)
the attached pcf8574a.txt file is really a salea logic data/setting file and should be renamed to pcf8574a.logicdata , if you don't have a salea logic analyser you can download the software from salea logic and view the complete data
It is the current device.

The PCF8574 and PCF8574A are identical, except for the different fixed portion of the slave address. The address used is 78 which fits with it being a PCF8574T and you use $78 which again fits with yours being a PCF8574AT.