modbus rtu communication as slve

 Yes I am sorry I read it wrong.

Okay, I opened it but didn't find the mode you were talking about.

Here's my screenshot.  I am sorry I am kind of new to communication.

I will forget about the master for now.

Thank you so much for your help

Duris_I

IMPORTANT!!!!

not change in Master MODE 4, read again what I wrote. In MB_COMM_LOAD instance DB (check in System blocks) which is to Slave depended, there is MODE which need to be set to 4. After change you need recreate sequence again - from COMM_LOAD REQ. Better before put PLC to STOP and RUN and then change first MODE and run COMM_LOAD. I think this is problem. PLS we still solve Slave system not Master, forget all about Master now.

 I will try this tomorrow and feed you back.

Will also check - with your help- mode of instance data block.

We will re-visit the whole thing tomorrow.

Thank you so much once again.

Duris_I

Hello,

ok but this is problem, your modules are RS-485/422 and your PC has USB to RS-232 adapter. In this case this is impossible. This is complete problem, we found it. You need USB to RS-485 adapter. This is your main problem and solution.

No problem,

pls try find that MODE inside this DB and check it if have 4 value. If not set it. But you need have that other adapter. Pls don't plug that cable between PC USB and PLC port, you can burn circuits. Bye...

Update: I've little bit investigate that instance DB and find that you're probably use instructions versions 2.x not 3.0 so there isn't MODE static variable. Only this hint.

Dear Duris,

Thank you for your help.
I have read your edit.

Should I try to use instruction version 3.0 ? If so, how shall I do it ?

We have retried today using the proper converter. Still no luck. Same scenario.

I will try tomorrow to remove all blocks and only have the modbus comm load and modbus slave blocks. Just to have a safer environment to test and see what it wrong.

Any advise regarding this ? OR any other pointers to check ?

Best Regards

Fadi

Hello,

not necessary use that v3 instructions. Yes, i recommend for init test use speed 9600, only one COMM_LOAD and SLAVE instructions with defined correct memory addresses and make tests. Next tip prior make Modbus tests is check PC USB adapter functionality (better with other adapter via Terminal SW), without this working you can't be lucky in next tests with PLC. Next problem can be cable between PLC and PC USB adapter, you need check in your CM module help pins arrangement to correctly wire with PC. Generally, it can be twisted pair used and 2 wires Data+ and Data- connected, of course swapped between both ports.

Update: sry, forgot your other questions. With v3 instructions can be used other new functions, can be useful, check this in help. If you want use them, you need only add new blocks with their instance DB and disable previous blocks. In case of problems, delete previous blocks with also system block DBs, FBs and add new blocks with complete cfg of parameters.

Okay.

I tried a whole new program, just to test the slave function.

I think right now the problem is with the MB_Holding_reg input.

I was first inputting the data block I want to fetch data from or write data into.

I had a status 8187.

The example on siemens website shows that I must use the "typeMbHoldReg" in DB BUT, I have error that this data type no longer exists.

So I tried to address the data block differently. There was still some trouble.

I read on some thread that I must have the data inside the DB in word format and I had them as int.

I now have status 7000, which is idling.

I am using a simulator so I am sending requests, and receive no responses and so a timeout error.

 I am attaching this sample program if this helps.

--Deleted Link--

Fadi Maximos

Okay.

I tried a whole new program, just to test the slave function.

I think right now the problem is with the MB_Holding_reg input.

 

I was first inputting the data block I want to fetch data from or write data into.

I had a status 8187.

The example on siemens website shows that I must use the "typeMbHoldReg" in DB BUT, I have error that this data type no longer exists.

So I tried to address the data block differently. There was still some trouble.

I read on some thread that I must have the data inside the DB in word format and I had them as int.

I now have status 7000, which is idling.

I am using a simulator so I am sending requests, and receive no responses and so a timeout error.

I only have one LED flashing, which is always on the other side than the PLC.

Is this the only problem we have ?

any other trouble with the software and the implementation ?