Reading Modbus registers on M172

[Anonymous user]

Hello guys,

I've got a problem with M172 07-18 (668.11 firmware) as modbus master.

I set RS485-2 as Master.

I made devices with registers by modbus custom editor.

I added those devices under RS485-2.

I assigned those registers to created "status variables".

Compiled and downloaded plc code with 0 errors and 0 warnings.

When I open programing tab and drag variables to watch window - all values are 0.

For the test I was connected those devices to AS-P and every values was ok.

On external modbus tester same - all registers read ok.

I am sure devices are ok.

I need help and out of ideas.

Thank you in advance!

[Ismet_S]

Hi,

Please check the status of the Target Variables "sysMbMrtuNodeStatus" to see if the communication between your M172P and the Device is ok.

BR

[Ismet_S]

[Bastian_Schmitz · Accepted solution]

You have to check if you made a download all. If you transfer only the Application you did not write the CONNECC.Par File which mange the Modbus Master. In that case the master function did not work in the backround.

You can analyse the status of the connected modbus slave like Ismet explained.

If the connec.par is missing CFG value would FLASE.

The position in the array show the Node number not the modbus address.

And you can check if you have read out the values of the slave based on register addresses which start by 0 or by 1.

If you use in that case the "false" address you will get CFG and PRES True but the value of the misscounter will be rise.

Via STATE you will the the Modbus Response which can show you were the problem could be. 

[Anonymous user]

Hello,

Thank you guys.

Download all button solved problem.

I've got comunnication with devices.

[Bastian_Schmitz]

Sounds good that your problem is solved. 

If you adapt you project in the future you will get sometime to the point that the download all need to much time (espaecially if you use integrated HMI).

In that case you have the additional way to download the CONNEC.PAR also seperate. 

To reach this go to Commisioning.

and make a right mous click on CFG files.

With this way you can download the CONNEC.PAR file alone.

That could save time in testing.

But generally use Download All.