When both the COM1 port and the COM2 port have the RS-422/485 setting,
RS-422/485 cannot be used for COM1 with SP-5B00(Standard Box). In this case,
replacement to SP-5B10(Power box) is required.
4.2. Signals of COM ports
At the time of RS-422/485 communication, the signal and the pin array differ
between the COM2 port on GP-3750T and the COM2 port on SP-5B00 (Standard
box).