Thanks for the reply. Sounds like I can use a RJ11 (phone) cable and add a RJ-45 connector or vice versa. Did you mean (see underline) GE M91 2 4 3 3 5 5 I was looking for the picture you mentioned and could not find the RS232 topic.
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?