Modbus RTU communication with Panasonic Minas servos

[Ariah 2]

I'm using a Mitsubishi FX5UC PLC to control some Minas A6S servo drivers. Previously I've always used a pulse train and discrete IO (it's the way things have always been done here). This time I'd like to use Modbus RTU over RS-485. I'm pretty confident that the RS-485 wiring is correct because I'm getting an exception code back from the driver rather than the messages from the PLC timing out.

 

I've been reading the manual called Operating Instructions (Overall) for the MINAS A6 series, particularly the communications supplement. I may be misunderstanding this, but the Modbus implementation appears to be non-standard. Specifically, in Schneider-standard Modbus, after the slave ID (or in this case, axis ID), the next part of the message is a function code that specifies the type of command; 01h is to read a coil, 05h is to write to a coil, and so forth. Whereas the Panasonic manual describes a different list of commands - to read the driver serial number it would be command 0, mode A, which gets transmitted as A0h. Documentation screenshots are attached.

 

The PLC function ADPRW only works with standard Modbus commands. So what I'm wondering is, am I misunderstanding the communications supplement, or do I need some code specifically for these drivers? If the latter, I would assume that someone has already written a function block or a predefined protocol definition for this hardware. Does one of you fine people have one?

 

Thank you in advance for the help!

[pturmel 167]

That doesn't look like Modbus at all.  RS-485 is just a signalling standard, not a protocol.  Are you sure the device supports Modbus?

[Ariah 2]

In case someone wanders in from Google, here's the answer.

The manuals for the Panasonic server drivers only describe how to control the devices via Panasonic's proprietary communications format. For actual Modbus communication, you need the document called "Technical Reference - Modbus communication and Block operation Specification". Here's a picture of the version for Minas A6S.