Modbus Merlin Gerin PM820 to Prosoft MV156MCM


Thread Starter


I am trying to read Holding registers starting at 31100 but getting no data back into my MV156MCM memory map. The PM820 manual says to read registers 1100 onwards with either a 30000 or 40000 register offset. I have other devices on this link that are working. Has anyone networked these before? Any tricks to check for?
Does the master time out or get an exception response?

It always pays to check the serial setup:

default settings are for the PM820 are
1) Protocol: Modbus RTU
2) Address: 1
3) Baud rate: 9600
4) Parity: even

Your MVI56MCM is already reading other multidrop devices. What are its serial settings?

Have you tried swapping + & - lines ?
note in Prosoft manual:
"RS-485 and RS-422 Tip:
If communication in the RS-422/RS-485 mode does not work at first, despite all attempts, try switching termination polarities. Some manufacturers interpret +/- and A/B polarities differently." pg 56 pdf.

PRT2 & PRT3 jumpers are presumably set to 485, Setup jumper is NOT jumpered, since you already have drops functioning ?

thanks for the reply David.
I have already setup the baud rate, address etc to match the prosoft card and have changed the Prosoft jumpers to RS485.

To test it further I will try to read in a single register as opposed to the whole block of registers as I have heard that if you ask for a register that isnt available the device may through a tantrum and send back nothing.

If this fails, i will try to reverse the polarity on the PM820 as you suggested.


Bernard Mansey

Hello Danny,

Since the PM820 is a product of the PMC division of Schneider, you may want to consider contacting their support group directly. For your convenience, I attached here under the phone #s and email address you can use to reach them.
BTW, I am PMC Global Support Manager, and I look forward to having my team assist you with this issue.

Best regards,

PMC Global Technical Support Email:
[email protected]
Local PMC support phone numbers :
Asia: + 852 25 79 95 68
Europe: + 33 4 76 60 62 35
North America: + 1 250 544 3010 (Global 24x5 Support number)