Serial Communication Between PLC and Raspberry Pi

ClimateController · Feb 8, 2015

Hello. I want to establish serial communication between the S7-300 and a raspberry pi. Toward that end, I'd like to begin by sending a simple 1 or 0 and have my PLC react accordingly. So I suppose you could say I want to use the raspberry pi as a switch. This is for testing purposes. I can transmit data from the raspberry pi via C++ or Python but I have no idea how to incorporate data received serially by the PLC in my ladder logic program. How can I accomplish this in Siemen's TIA Portal V13? Is there a block or instruction that I can insert into my ladder logic program and it will read the serial port? Thanks for the help in advance.

Onstege · Feb 8, 2015

Modbus RTU is a simple and straightforward protocol. I'm not a Siemens guy, but it would surprise me if your PLC doesn't support it.

ClimateController · Feb 8, 2015

The S7-300 does support MODBUS. However, I cannot figure out how to implement that in the software. I am just a beginner as far as Siemens is concerned so I am having a hard time figuring out some of the more specialized stuff in the software.

ndzied1 · Feb 8, 2015

For 35 Euros you can implement a CoDeSys PLC in your RPi.
http://store.codesys.com/codesys-control-for-raspberry-pi-sl.html

If with your testing you are OK with a 2 your timeout, then it is actually free.

I have played around with the Modbus/TCP which works great. I know it also supports Ethernet/IP but I haven't played with the Modbus/RTU but there is a pretty good forum for support:
http://forum.codesys.com/viewforum.php?f=21

I don't think it supports the /RTU directly but there is some mention of it on the forum.

ClimateController · Feb 8, 2015

Thanks for the replies, everybody. As it turns out, this is what I am trying to do: https://www.youtube.com/watch?v=Z77ZVjPIiA8

Apparently, it's called freeport communication.

I have watched the video but I still cannot figure it out in TIA Portal V13. Would greatly appreciate some help.

KalleOlsen · Feb 8, 2015

Hi!

I am not familiar with TIA, but have used Step7 since it appeared back then.

The Youtube example is not relevant, as it shows an S7200 that is incompatible in all ways to your S7300.

In the S7 300 you will need a serial communication card like CP340 or CP341. Set it up with corresponding line speed, character bits, stop bits and parity. Use fhe function blocks BSEND and BRCV to write and read data.

Kalle

boneless · Feb 8, 2015

Do you need serial, or do you have an ethernet interface?

Snap7 is a library which would allow you to do what you need:
https://www.facebook.com/snap7.project?ref=br_tf

I have done a little testing, and it works pretty well.

ClimateController · Feb 8, 2015

@Kalle
Thanks for pointing me in the right direction. I was able to configure TIA Portal and PLCSim to emulate an S7-300 PLC with a CP-340 card but I don't know how to put that to use in the ladder logic program. Cannot find the commands/instructions you mentioned. Got the software from uni. Maybe my license is limited in that I do not have access to all the blocks?

@boneless
The PLC at university does not have ethernet support sadly. Stuck with an MPI to USB adapter.

boneless · Feb 8, 2015

So you want to communicate with a Siemens PLC using the USB-MPI adapter?

A quick search turned this up:
https://github.com/xvzf/linux-raspberry/blob/master/drivers/usb/serial/siemens_mpi.c

From there you could run an OPC server:
http://www.openopcua.org/

Might be worth a shot. I don't think you would be able to do it with just the USB-MPI adapter and CoDeSYS, but I can be very wrong.

Looks interesting, keep us updated!

ClimateController · Feb 9, 2015

Thanks, boneless. I understand MPI is based off RS-485 so I can treat the C++ or Python program as normal serial communication, right? Access the USB port, configure the baud-rate etc. and send my data?

boneless · Feb 9, 2015

Theoretically, maybe. I don't know a whole lot about serial communication, but as I understand it, MPI is a proprietary protocol, and I have not seen anybody successfully dismember it. But I can be very wrong

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Serial Communication Between PLC and Raspberry Pi

ClimateController

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Onstege

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ClimateController

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KalleOlsen

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boneless

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boneless

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boneless

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