The protocol that we are goining to use is modbus and cable RS485 (4 wires). The printed circuit board is goining to be programmed in C language.

Floowkid

Hi,

I was asked to write the program where S71215 with module CM1241 is goining to comunicate with many printed circuit boards to open and close doors and turn off/on lights (digital input and output). Every door will have only one circuit with it's own address. 

The protocol that we are goining to use is modbus and cable RS485 (4 wires). The printed circuit board is goining to be programmed in C language.

This is will be my first experience with modbus. Please could you indicate me which is the function in TIA portal that i should use for this kind of application? Maybe there is an example on internet?

The C programmer asked me as well if Siemens modbus let me use ASCII or just RTI.

Hi Kid,

Which 4 wires would you want to use exactly?...

You are looking for Modbus RTU over RS485.
Unless it is Modbus ASCII you are really looking for.
Or perhaps Modbus TCP over an Ethernet link.
.... make sure what you need.

I would recommend you do some homework first.
Start here for Modbus RTU:
https://support.industry.siemens.com/cs/search?search=modbus%20rtu%20s7-1200&type=Faq&lc=en-WW

In the above link you will find also an example for S7-1200 to S7-1200 link with Modbus RTU. Concentrate on the MASTER.

You also need to work out which "registers" are going to be made available on the pcb side.

I hope this gets you started.
You are more than welcome
to browse through existing Forum answers
or to return here to this post.

w

Hello,

only addition to William's great info, I can imagine C programmer side. Really I don't know what kind of library (or maybe own implementation of Modbus protocol) he will use. Maybe from this point you can start, ask him again what protocol he want implement (Modbus RTU or Modbus ASCII). If not clear idea is on your side look also to this perfect help:

http://www.simplymodbus.ca/index.html

Here you can see all needed infos, also protocols, examples. Look, you have implemented RTU libraries on S7-1200/1500 with your CM1241 module, mean Master and Slave. But also this information who will be what - Master or Slave, probably also needed ask to your other side programmer for sure. You can give to us next infos.

Have I ever told you -
I like seeing you in that platinum colour!

Duris_I

...Master or Slave...

To be fair to  <Floowkid>  .. 
let us not have him discover this fact by himself
the S7-1200 must be the Master in the network.

Also... be sure that there is a limit to the wire distance and partner count.

Floowkid

Hi,

I was asked to write the program where S71215 with module CM1241 is goining to comunicate with many printed circuit boards to open and close doors and turn off/on lights (digital input and output). Every door will have only one circuit with it's own address. 

The protocol that we are goining to use is modbus and cable RS485 (4 wires). The printed circuit board is goining to be programmed in C language.

This is will be my first experience with modbus. Please could you indicate me which is the function in TIA portal that i should use for this kind of application? Maybe there is an example on internet?

The C programmer asked me as well if Siemens modbus let me use ASCII or just RTI.

 Hi 

please refer below links for more more details of modbus RTU in s7-1200 plc

modbus 1200 forum

this link also help you in modbus programming

modbus

also refer attached program

all the best 

Hello everyone,

Thank you for all materials.

After many test we decided to use RS485 protocol (SEND_PTP, RCV_PTP ) as for the programmer that use embedded system it was the easisest solution.

In this moment we face the last problem. When i use SEND_PTP the PLC add string header to each package.

In attacched you can find print screen with detail of my problem. Is there any way to cut the header or shift the all package?

I have found this articale as the solution but it didn't work out for me. https://support.industry.siemens.com/cs/document/42002283/how-do-you-compensate-for-the-string-mismatch-caused-by-the-rcv_ptp-and-send_ptp-blocks-?dti=0&dl=en&lc=it-WW

Hello,

check also pls again SEND instruction and it's parameter about buffer pointing. You need maybe point only to offset, not also define BYTE 6 length. How much BYTEs you want send, you define in LEN parameter, here you have good value -> 6.

Update: you can for sure check incoming message with some PC application like Hyperterminal and see if you make that problem, situation that Kaulquappe sugested to you or problem with your used PC application.

Dear All,

I want to send 6 byte.

All tests that i did so far are tests where package is send from PLC through USB / RS485 converter to simulator terminal on Simatic PG.

Please look at attached for details.

I tried to use as well PORT_CONFIG, SEND_CONFIG, SEND_P2P and also in that case i have header 00.

ps. Parity should remain as "None", in other case the programmer of the device should change all his software that is written for pure RS485.