I have a M91 Unitronics PLC (M91-T4-R6-ZK1 serial HB21006HN4002G) which has a RJ-11 port for RS-232 Modbus communication.
I have a GE PLC which has a RJ-45 port for RS-232 communication with following pin readout:
1.RTS
2.TxD
3.RxD
4.
5.Com
6.CTS
7.
8.Com
Is a adapter kit required?