UPDATE : PROBLEM SOLVED

Hi guys,

just to keep you updated I solved the problem. As you mentioned MB_COMM_LD needed to be call just one time (at startup, in Startup OB). I made a mistake because in S7-200 you need to call port initialization every scan. Also I added few networks to catch done and error bit and status word. You need to careful how you are defining DB for data exchange, it need to be non symbolic and you need to know what data type slave is sending. In my case PAC3200 is sending floating point data so I used DB with struct of floating point variables.

Once again many thanks for answers and help.

Cheers

Alen

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Hi guys,

in my recent project I need to use Siemens S7-1214 controller to communicate with the Sentron PAC3200 device using the Modbus RTU network. Previously, for the same purpose, I was using S7-224XP controller and there were no problems, the communication was working spotless (instruction library blocks were used). Unfortunately with the new controller I’m not able to establish communication.

On the beginning please let me introduce you with my hardware configuration. As mentioned, there is S7-1214 controller expanded with the CM1241 (RS485) communication module. The RS485 port is configured as a Modbus Master and connected with the Sentron PAC3200 device (expanded with the RS485 module).The TIA online diagnostic shows that controller and RS485 module are OK (healthy).

Configuration of Modbus port on the S7-1214 controller is carried out using MB_COMM_LD library block according to the S7-1200 system manual, please find attached TIA project. According to the status word the port configuration is executed without any error. The CM1241 port baud rate is set to 19200, no parity, 8 bit per character and 2 stop bits which correspond to the settings of the PAC RS485 port (19200, 8N2).
The data exchange with the Sentron PAC3200 device should be carried out using a MB_MASTER block, please find attached TIA project. For the test purposes I wanted to read 6 registers (words) from the slave holding registers, starting with the address 40002, Fig.2. The data block for a data exchange is configured according to the S7-1200 system manual. With the positive edge of the M20.0 bit a data exchange should be started (I’m forcing M20.0 to “1”). The Busy bit is ON for the few moments (less then 0.5 sec) as well as the TX led on the CM1241 module, but after that noting happens. There is no indication that job is done or that some error is occurred (error bit and status word are zero). Also there is no timeout error eventough timeout time is set to the 1000ms. The error in the cable or connection should be excluded because the same PAC-cable-connector configuration is working fine in combination with the S7-224XP controller. At the end, even if some cabling/connection/parameter errors exist it should be concurred with the appropriate error from the MB_COMM_LD or MB_MASTER blocks.

Please find attached simple TIA project which I was using for the Modbus communication test.

Hi Robster,

many thanks for the quick answer.

1. It make sense, I will put it in the startup OB and try it. Maybe cyclic calling of the port initialization is doing some problems.

2. Will try it also to see if done bit can be catch.

3. I know this from the system manual. I was waiting allot but nothing happened, my DB was empty, no comm. error indicated. Don't know maybe something is wrong with the settings of the RS485 port (it is not matching slave configuration), but I check it many times and I don't see what could be wrong. Same slave is working fine in the combination with 224XP, tried yesterday. Obviously some comm. settings on the 1214 and slave are not the same.

Cheers
Alen

Hi Abyrne,

I'm monitoring allot of different values form PAC. Sorry I have no time to analyse your TIA project because I'm running away for holidays. I noticed just that for data exchange I'm using struct of floating point data. As you can see from my project I'm monitoring 9 values and don't have any problems. Take a look of my simple project. I added few networks to catch status bit so ypu can see which error code you have. Maybe your timeout time is too small so when you try to read bigger stream of data timeout error occurs. Try with my project, hope it will help.

Cheers
Alen