Enron Modbus Client on EPIC

groov EPIC
1

Reaching out for some help.
We have a project which requires us to obtain data from some Emerson Flow Computers. Unfortunately, these use Enron Modbus as their protocol.
I have looked for ways of getting this data intto Codesys running on EPIC PR1, but there is no Codesys driver!
No driver in Ignition nor Node-Red that I can find either.

Anyone got an idea on how to achieve this using either Ethernet or RS485?

2

I had never heard of it, but a quick Google showed this:

I think you can just use the Node-RED node and fix it on the back end.
@philip would hopefully have some thoughts on this.

3

Yes, that’s the beast!
I have used all sorts of Node-Red Modbus flows to achieve this, but have hit a brick wall with them all.
The nearest I got was using node-red-contrib-modbustcp, but it seems to use its 2nd byte as a message counter.
As an example, if I want to read a single float (32-bit in a single register) at register 7003, slave ID 100, using FC3 the transmit should be:
00 00 00 00 00 06 64 03 1B 5B 00 01
but this flow transmits:
00 01 00 00 00 06 64 03 1B 5B 00 01,
Next time:
00 02 00 00 00 06 64 03 1B 5B 00 01,
etc.
So close, yet so far!

4

If you are desperate, I have written a partial Modbus RTU serial 485 in CodeSys. I believe someone else’s fully tested and more functional solution would be a better choice. But if your stuck let me know. I could send you the code.
Using the SysComOpen, SysComSetSettings, SysComRead, SysComWrite functions.
Read only - coils, discrete inputs, holding regs, input regs. Supporting types bool, int16, uint16, int32, float.
It is written pretty generically.
Dave

1 Like
5

Hi Dave,
I welcome your offer. It will be a starting point, which I don’t really have at the moment.
Thank you for your reply.
Darran

6

If you can get it going in Codesys, that would be good since that is where you want the data. If you want to try it in Node-Red, here is some test logic I have that makes an OptoMMP request for inspiration. (I don’t parse the response in this sample though). The same thing could be done to make a modbus request (it is a fairly simple protocol).

image
image946×193 13.8 KB

Build MMP packet node (you would need to modify to represent the modbus protocol)

//OptoMMP packet
mmp = {
    dest : 0,  //16b always 0
    tl : 0,  //6b optional
    rt : 0,  //2b always 0
    tcode : 4, //4bits
    pri : 0, //4b always 0
    source : 0,  //16b optional
    offset : 0xFFFFF1001900, //48b address
    length : 0, //16b only on blocks, specifies byte length of data section
    extcode : 0, //16b always 0, only on blocks
    data : 0 //varies, fixed 32b on quadlet response
};

mmp.tcode = 4;
mmp.offset = 0xFFFFF1001900;

msg.mmp = mmp;

return msg;

Take the data and turn it into a byte array to send by using the javascript Buffer library:

const buf = Buffer.alloc(12);
pos = 0;

pos = buf.writeUIntBE(msg.mmp.dest, pos, 2);
pos = buf.writeUIntBE(msg.mmp.tl << 2 | msg.mmp.rt, pos, 1);
pos = buf.writeUIntBE(msg.mmp.tcode << 4 | msg.mmp.pri, pos, 1);
pos = buf.writeUIntBE(msg.mmp.dest, pos, 2);
pos = buf.writeUIntBE(msg.mmp.offset, pos, 6);

msg.payload = buf;


return msg;

Since it is poll response, I just feed to the TCP node. The response will then need parsed to get the data you need. The Buffer has read classes for this as well.

7

Hi @SDUK I am new to Opto 22 and Codesys. I have same issue, we have pressure transducer that is using Enron Modbus, trying to find solution. Did the issue got resolved ? do you have any solution for this?

8

Hi Naveen,
This was many sleeps ago :sleeping:.
I do remember finding a possible solution for our client:

I never heard back from them, so I am not sure if they used it or used standard Modbus.