A Usefully Tool

The below wiring diagram shows the QJ7MB91 modbus card linking to the RS485 port on the Comap unit of the CHP. Noting that the Comap unit needs to be set to RS485 as well.

Noting the setting on the Comap where 9600, none, 8 bits and one stop bit. With the PLC working as the master unit.

The comms switch are broken down in page 159 of the manual, but a rough overview is below.

• Switch 1 and 2 are used for Modbus over RS232
• Switch 3 – set to all 0000 for master on the network
• Switch 4 bit 1 and 2 (05) determine the speed of the comms
• Switch 4 bit 3 and 4 (04) determine the other settings (parity, stop bit etc)
• Switch 5 determine the modbus address (bit 1&2 for RS232 and bit 3&4 for RS485), if master these should be set to 00.

Since the PLC is operating as master on this network, if set correct you’ll get the SD, and RD (because their link) lights flashing as well as the NEU.

A useful link is to Mitsubishi card search results.

I’ve also link in the manual here: QJ71MB91