Here are the steps we use to troubleshoot RS-232 communications:
- Swap pins 2 and 3 on the DB-9 connector or Tx and Rx on the control processor, where applicable. This solves 99% of the issues with RS-232 communications.
- Verify make/model of the gear between the installer and the programmer.
- Confirm the port location on the processor.
- Confirm the comm settings such as baud rate, parity, stop bit, data bits for the device.
- Confirm the physical pinout of the RS-232 cable is correct. Using pre-fabricated cables may cause issues if the device uses pins 2, 3, and 5 only.
- Try to use a terminal emulator (e.g. Terra Term) to send commands manually to the device from your PC.