I just installed a new HAI Omnistat2 RC-2000 in my home and it works properly as a standalone thermostat and drives my HVAC system consisting of a single-stage gas furnace, humidifier, and AC unit (December in Montreal so the AC unit remains untested). However, I'm having difficulty establishing serial-communications between it and my PC's Home Automation software (i.e. it is not connected to an OmniPro panel).
- I made a serial-cable as per Appendix B of the "Serial Protocol Description" document. For a DB-9 Female connector:
Pin 5 (GND) connects to N/C.
Pin 2 (RXD) connects to BLACK.
Pin 3 (TXD) connects to GREEN.
Pin 4 (DTR) connects to YELLOW.
Pin 4 is also shorted to pins 1 and 6.
Pin 7 is shorted to pin 8.
FWIW, I triple-checked the serial-cable connections and I'm confident the cable and connections are fine.
- I removed the u-shaped jumper from the right-hand connector as per the instructions on page 15 of the document.
- I left COMM Jumper J8 in place.
- I set the System Baud to 300 and left the Expansion Baud at the default 1200.
QUESTION: What is the difference between these two parameters? Which one is for communications with a PC? I'm assuming it is System Baud.
- The serial-cable is connected to a Digi EdgePort/8 which is an 8-port, USB-to-serial-port device. It is seen as COM6.
QUESTION: Could the thermostat be unhappy with the TTL-level voltages (5V) furnished by USB/serial-port converters? Must it see 12V?
- I set my PC software to drive COM6 at 300 baud, 8-bit, no parity, 1 stop bit.
- My PC software allows me to observe serial-port communications. Transmitting a "Poll for Group 1 Data" command ("010203") results in no reponse from the thermostat, not even a "Negative acknowledge". As an experiment, I changed COM6's Baud Rate to 1200 but it did not correct the problem.