Siemens 545 MODNIM

[Tim Ganz]

I am working with a Siemens 545 PLC and the MODNIM Modbus module and I am trying to figure out if the module is a Master or Slave. It does Modbus Ascii and RTU and is set up for RTU. I am trying to use a Modbus gateway on the other end that goes from RTU to TCP but on the serial side the gateway can be set for RTU master or slave and the manual does not seem to call it out.

Does anyone ever have any experience with this module or 545 PLC?


MODNIM Manual

https://cache.industry.siemens.com/dl/files/913/17516913/att_76257/v1/505-8122-1.pdf

PLC Manual

https://cache.industry.siemens.com/dl/files/465/17518465/att_106091/v1/545-8101-2.pdf

 

[Steve Bailey]

Based on the diagrams and the lack of any parameter settings to select between master and slave, I'm of the opinion that it will be a slave.

 

[Ken Moore]

I have used several of these to connect TI-PLC's to a Foxboro DCS, way back when. The MODNIM is always a slave. No other option. If you look at the network drawings, the HOST (aka Master) is never the PLC.

It has been awhile, but one gotcha I remember is the offset. The 545 starts programming at C1 or V1 as the first coil or first memory register. But when you use the MODNIM to read values the values start at zero. So if you want to read V100, you have to request V99....

Another tidbit, TI-PLC's used the same memory area for inputs and outputs, so if you had X1-32 as inputs, you could not have Y1-32 as outputs. One would overwrite the other. So you would have to have the outputs as Y33-64, a lot of effort used to be spent planning your memory assignments. However, because of this you can read inputs and outputs via the ModNim with one request. In my example if you requested X0-63, you would get the Y values too.

Good luck.

 

[Ken Moore]

BTW,
CTI makes a newer version that supports Master and Slave configs.

https://www.controltechnology.com/p...2573-MOD-Serial-Interface-Adapter-with-MODBUS

 

[sigmadelta]

From the Siemens MODNIM Manual:

 

[Tim Ganz]

Thank you all for your assistance. This will be most helpful.

 

[MeredithB]

Tim -- On behalf of CTI, please feel free to reach out if you need any additional help with the problem you are trying to solve or if you'd like more information on our products that are fully compatible (but newly manufactured!) with the 545 PLC/505 series.

https://controltechnology.com/contact

If you are indeed located in Dallas, reach out to Ron Soderberg. Or feel free to reach out to me directly. mbroome@ the above domain.

Good luck.
Meredith