Infinity Protocol Hardware

Proprietary ABCD port is really just RS485 serial(AB) and 24VAC(CD).

Port	Suggested Color	Function
A	Green	RS-485 D+
B	Yellow	RS-485 D-
C	White	24v AC Common
D	Red	24v AC Hot

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	Cheap ch341/max485 based RS485 adapters like this one are known to work
	This FTDI adaptor also works and has the advantage of a ground connection, removable terminal block, and easy-to-access intermediate TTL points

The author has also gotten a cheap MAX485-based rs485/ttl converter working along with an esp8266 board (nodemcu)to provide a wifi/tenet serial bridge to rs485 data. The esp8266 can also decode/encode frames in real time. Seen here lovingly mounted, hanging in mid-air, from its own wiring:

Be aware of RS485 adapters may use RS232 lines to drive the transceiver mode. If this is true, disconnecting the software on the PC may drive the RS485 chip to transmit mode and stop all communication on the bus. If this happens an error will show on the thermostat, but will go away if you remove the RS485 adapter from the bus.

Miswiring can also lead to trigger the same fault, by disconnecting the adaptor from the bus, the fault is going to be cleared.

Also connect the adaptor with the existing wires, do not use any jumper cables, the gauge is most likely not the same and they are not twisted. That could also lead to some errors.

Serial data is 38400 8N1 and is mostly the thermostat sending requests for data and the air handler/outdoor units replying with it.

Please submit your own logs and contribute to the list of devices and registers in this wiki.