Gefanuc pcm301

If you will be using RS232, you will use at minimum, pins 2, 3, and 7. Whether or not you need to connect the others depends on the requirements of the IED 850.
If you will be using RS485, the the A designation of a pin denotes -, the B designation denotes +. The ' designation denotes outgoing data direction. Lack of a ' denotes incoming data.
Your choice of whether to use RS232 or RS485 will likely be dictated by the IED 850. It may only support one electrical connection standard.
If the PCM301 module is to be the Modbus master, you will need to have MegaBasic program running in it. That program will need to include instructions to control where in the PLC's memory the Modbus data resides.

Thank you a lot Steve!
my IED uses modbus port as shown in the photo! but on the pins of the rs-485 port 2 cable I can't identify which would be the A+ and B- pins. I've tried several possible combinations! to configure the pcm301 I'm using TERMF and I send two files that look for the port and word configuration in the cpu ladder! but I'm also having doubts about the command to load the file from the pc to the pcm301, when I give the command @pc:x.bat an error message appears: file not found. but the file is in the root folder of the pc!

Wiring pcm301 comm

this is correct connection Steve?

Based on the diagram for 2-wire RS485 in appendix A of the PCM manual, I suggest jumpering pins 9 and 13 together at the PCM end and connecting to D4. Also jumper pins 21 and 25 together at the PCM end and connect to D3. Connect pin 7 at the PCM end to D5 as you show.