Duh that makes complete sense… Not sure what I was thinking. Thanks for the explanation. One other question. I am trying to get it to work using several PCF8574s.
I have the first I2C address set to 0x20 to tell the firmware that the version is 3.0. From my understanding, I cannot use any of the GPIOs on this chip for zones. Also without using this, If I hook up any other board, the ESP will not boot. So I have a second board with address 0x21 which is for AC driver and I can get it to trigger the first 8 zones, and the UI shows 8 zones available. Then if I hook up a board with address 0x24 which looks to be to address for the first expander board, the UI now says there are 24 stations available, but the GPIO on the 0x24 board drive zones 17-24. this continues on. each expander board with address 0x24-0/27 adds 16 more zones, but can only control 8 zones. I cannot get control of zones 9-16 no matter what I try. Is this normal?