Mitsubishi PLC with RS422 cylindrical port. Adding communication board can increase RS232 port.

However, the terminal definition of Mitsubishi RS232 port is the same as that of PC, 2: TX 3: RX 5: GND.

Omron's RS232 port terminals are defined as 2: TX 3: RX 9: GND.

In other words, the cable connection between Mitsubishi PLC and PC is 2-3; 3-2; 5-5 (the former is the port terminal connecting the PLC end and the latter is the port terminal connecting the PC end), and the cable connection between Omron PLC and PC is 2-3; 3-2; 9-5 (the former is a port terminal connected to a PLC terminal and the latter is a port terminal connected to a PC terminal).

Finally, we can look at the RS232 communication protocol, which is helpful to understand the communication port.