RS485 port A (COM1) and RS485 port B (COM2) each have two LEDs reflecting port activity.
Yellow (TX): indicates the controller is transmitting data on the RS485 port.
Green (RX): indicates the controller is receiving data from an RS485 device connected to this port.
These LEDs use a fixed “on time” when a message is detected on the port. If a receive LED is on constantly, this can indicate
a wiring problem, such as a shorted wire or reversed wiring.