1746 BAS 502 M0/M1 module

sandy5020

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May 2012
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vadodara
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Hi,

I am upgrading a AB PLc to Siemens PLC logic and everything is ready for siemens but the problem is the existing PLC is communicating to DCS via modbus RTU as slave.

I can see some alarms and data from N10:0 register moving to M0:1.1 with a length of 50 file and from DCS M1:1.1 data moving to register N10:22 with a length of 1.

I wish to know the modbus address of this is it like N10:0=40001 and N10:22 = 400022 ?? as I need to do the same in siemens PLC with the help of modbus module

Regards
Sandy
 
The 1746-BAS is an old BASIC52 system-on-chip with a backplane interface and API.

ProSoft Technology used the same hardware to build many of their serial interface modules, including the "MCM" Modbus communication modules. Every once in a while you'll find a module with the 1746-BAS label that has been loaded with the ProSoft MCM firmware.

So Step 1 is to figure out if this is a true Modbus module, or if it's a BASIC module that's implementing Modbus or another serial protocol.

If it's truly a ProSoft module, then you can use their User Manual to determine which M0/M1 buffer addresses correspond to what Modbus registers, based on how the module is configured.

If it's a custom program running on a 1746-BAS, then you'll have to connect with a serial console and LIST the program to read it, then start analyzing that program.
 
Hi,

i am sure the protocol is Modbus RTU slave as there is ladder logic in the PLC program for data transfer via modbus.. I just need to know the addressing so that I can do the same with new PLC ie siemens with modbus module

Regards
Sandy
 
I will repeat: the 1746-BAS is not a "Modbus Module". It is a general purpose BASIC52 computer with a backplane interface.

If your is really a Prosoft "MCM" with a label that says "1746-BAS", then you can read the Prosoft user manuals to learn how the module works.

If not, then I cannot tell you how your particular module works, because it must have a custom program in it.

Try this: Go into RSLogix 500 and open the I/O Configuration window.

For the slot occupied by that communication module, does it say "1746-BAS" (or some variation of that) or does it say "OTHER" with a Module ID number ?

That will at least tell us what type of module the controller thinks it's running.

Power down, remove the module, and examine the module very carefully for the ProSoft part number "3150-MCM".
 
OK, good.

So we know it's either a true 1746-BAS with custom firmware in it, or it's a Prosoft 3150-MCM with the wrong label. Both of those modules will show the "1746-BAS 5/02 BASIC module M0/M1 capable" in the I/O configuration.

My next step would be to connect to the console port with a serial terminal emulator program (I prefer RealTerm) and see if the module reacts like a Prosoft module or like a BASIC module.

You can read up on how to connect to the console port in the user manuals:

1746-BAS: https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1746-um004_-en-p.pdf

Prosoft 3150-MCM: https://www.prosoft-technology.com/...kwell-Automation-In-Chassis/3150-SLC/3150-MCM
 
Hi,

Thanks for the reply, I understand the details should be collected from the module but the problem is machine is running and the customer will not allow to touch the existing one we have already uploaded the program before some months during a major shutdown. I have only two option either to understand the mapping from the RSlogix program or from the DCS program.

My final concern is to map the addressing with siemens s71200 plc as modbus rtu slave, program has been created for the siemens now I just need to copy some tags to modbus for DCS.


Regards
Sandy
 
I have done similar system migrations in the past and had to use a protocol analyzer coupled with the monitoring software in the PLC controller to develop a map of PLC memory to Modbus registers.

If you can't disconnect the RS-232 port for even a few seconds, then it's impossible to put an analyzer in-line with it.

If you can, I very strongly recommend the EZ-Tap from Stratus Engineering in California. It's a passive serial tap that will fit in-line with an RS-232 port and allow you to connect over USB as though each port was a separate Windows COM port. You can use a sophisticated protocol analyzer like Frontline Test Equipment, or decode the Modbus frames by hand or with a helper tool like the Chipkin Automation Module Parser.

To my knowledge the old 3150-MCM modules don't have a runtime console that you can monitor while it's operating.

So to figure out how the module is set up, you'll have to examine the SLC-500 programm in conjunction with the 3150-MCM User Manual.
 

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