Modbus/TCP Client on S7-1200

Hello

I know that there are many topics related to Modbus/TCP, but i read the manual twice, folowed some tips from here, and had not succeeded.

I got succesful connection through Modbus Poll,

i´m using a S7-1215C CPU to connect to 3 types of dataloggers.

I set CONNECT parameters like on Modbus Poll. Checked "InterfaceId" on hardware configuration. Set "MB_Unit_ID" to 1. Created a routine for error treatment.

When REG is 1, block status keeps busy, and then generates and 16#80c8 error status

kindly ask the most experienced if they could see what i missed.

Best regards

Follows an attachment with screen prints.

Hello,

2 problems at your side but one is looks like very basic and due not careful check of set parameters as same as in PC app with correct functionality.

1. this basic wrong set same parameter to CLIENT block. Look at your PC app base register address - 30546. Now look to your CLIENT block 

2. now to probably wrong expected calculation and how to set correct address of destination register. You said that you've read documenattaion but inside documentation is clear that with read holding register is required to add 40001 or 400001 offset with expected register (it depends to standard or higher range addressing). In your case from PC app that you said is working, your CLIENT block address then requires higher range because expected base address is 30546 so then you need use formula - 400001+30546->430547 and this is your value you need set at CLIENT block. Be careful if you have enough long buffer to storage data after receive because you require in case of PC app 22 registers and inside PLC 20, this is also chaotic and not clear why that differencies. You can explain this also and also pls understand that use different test parameters can not go to proper help here.

Duris_I

Hello,

2 problems at your side but one is looks like very basic and due not careful check of set parameters as same as in PC app with correct functionality.

1. this basic wrong set same parameter to CLIENT block. Look at your PC app base register address - 30546. Now look to your CLIENT block 

2. now to probably wrong expected calculation and how to set correct address of destination register. You said that you've read documenattaion but inside documentation is clear that with read holding register is required to add 40001 or 400001 offset with expected register (it depends to standard or higher range addressing). In your case from PC app that you said is working, your CLIENT block address then requires higher range because expected base address is 30546 so then you need use formula - 400001+30546->430547 and this is your value you need set at CLIENT block. Be careful if you have enough long buffer to storage data after receive because you require in case of PC app 22 registers and inside PLC 20, this is also chaotic and not clear why that differencies. You can explain this also and also pls understand that use different test parameters can not go to proper help here.

  Thank you, Mr. Duris for your fast answer.

You were right, that information on manual passed me by. The issue was to add +400001 to the address on MB_DATA_ADDR on MB_MODE = 0, or put MB_MODE = 103. It worked for the equipment that uses function 03 of Modbus Protocol

But on the one that uses function 04 couldn't work on s7-1200, worked only by Modbus Poll again. I tested with MB_MODE=104 and MB_MODE=0 adding 30001 to the address with no success. This equipment works like a Modbus TCP to RTU gateway with many serial equipments, and i probably should vary MB_UNIT_ID to access then, but none of then answered. Same 16#80c8 error.

Any other tips on that call?

Hello,

user

But on the one that uses function 04 couldn't work on s7-1200, worked only by Modbus Poll again. I tested with MB_MODE=104 and MB_MODE=0 adding 30001 to the address with no success. This equipment works like a Modbus TCP to RTU gateway with many serial equipments, and i probably should vary MB_UNIT_ID to access then, but none of then answered. Same 16#80c8 error.

pls attach ZIP with screenshots from PC app to see your correct functionality cfg or PDF as previously, with FC04. CLIENT block Online parameters is good to see also. If Gateway is used, is very important to report this at init post and use properly configured MB_Unit_ID parameter for different serial line Slaves. This means that you can better stop REQ execution of block, change Slave ID and then set REQ again ON to continue with new Slave data exchange. You don't need disconnect because you're connected to one Server (Gateway) logically and need only collect data from serial side Slaves.

Hello,

As wished, screen prints attached. 

Tested on MB_MODE = 0 and 104.

Best Regards

Duris_I

Hello,

user

But on the one that uses function 04 couldn't work on s7-1200, worked only by Modbus Poll again. I tested with MB_MODE=104 and MB_MODE=0 adding 30001 to the address with no success. This equipment works like a Modbus TCP to RTU gateway with many serial equipments, and i probably should vary MB_UNIT_ID to access then, but none of then answered. Same 16#80c8 error.

pls attach ZIP with screenshots from PC app to see your correct functionality cfg or PDF as previously, with FC04. CLIENT block Online parameters is good to see also. If Gateway is used, is very important to report this at init post and use properly configured MB_Unit_ID parameter for different serial line Slaves. This means that you can better stop REQ execution of block, change Slave ID and then set REQ again ON to continue with new Slave data exchange. You don't need disconnect because you're connected to one Server (Gateway) logically and need only collect data from serial side Slaves.

 I had already made a code to stop REQ while changing MB_Unit_ID, but not using on the moment. Configuring the ID to 247 as shown on the attached fileon last post, i can access the own logger register map, as shown on Modbus Poll. But still having problem on s7-1200.

Does any other experienced problems acessing TCP servers using modbus function 04?

Best Regards,

Hello,

look, it's hard to help if you step every time you ask to different destination Modbus register. We didn't still solve your first problem and you are now asking to Input register area. Again, proper address set is mandatory so you need in this case (Input register) use formula 30001+8004->38005 <your register address>. Try to do everytime tests with MODE 0 and LEN 1, only read one register because then is really hard to think where you do problems. Next important, we still don't see your DB/memory area for incomming data storage. Proper structure (I expect in this case WORD elements) is required. Simply, you can have correct parameters set at test time but not correct storage place can fall to problems. Where you have conditions to check in case of error occured? Maybe you errors and you don't know about that and then you only guess where all is going. Other problem I see from your last PDF, you have there 2 CLIENT blocks. This is not correct and you will not have functionality with both set to true, logically. If you see there, block is blue outlined what can indicate problem with functionality/initialisation.

Duris_I

Hello,

look, it's hard to help if you step every time you ask to different destination Modbus register. We didn't still solve your first problem and you are now asking to Input register area. Again, proper address set is mandatory so you need in this case (Input register) use formula 30001+8004->38005 <your register address>. Try to do everytime tests with MODE 0 and LEN 1, only read one register because then is really hard to think where you do problems. Next important, we still don't see your DB/memory area for incomming data storage. Proper structure (I expect in this case WORD elements) is required. Simply, you can have correct parameters set at test time but not correct storage place can fall to problems. Where you have conditions to check in case of error occured? Maybe you errors and you don't know about that and then you only guess where all is going. Other problem I see from your last PDF, you have there 2 CLIENT blocks. This is not correct and you will not have functionality with both set to true, logically. If you see there, block is blue outlined what can indicate problem with functionality/initialisation.

 Hello Mr. Duris

The problem on first post was solved, the address/mode was wrong, and i thank you for showing me that. On this device the connection is working

But I couldn't have the same success with another device on same network that need to be acessed the input registers (Modbus FC04) by s7-1200.

i´m using only 1 MB_CLIENT block and a 127 word array as incoming data storage.

For knowing when a erro occurs, i move the status word when ERROr = true

Screen prints attached.

Feel free to advise me the way to make easier to help me.

Best Regards

Hello,

thank you for good description what you've set. If I see your last CLIENT block, I see it correctly configured so problem can be with change of devices in your code. I recommend to do it manually for first, simply do change on Client block parameters like REQ and DISCONNECT manually via Watch table. Pay attention that no code can affect any this parameters. As your TCP Server is Gateway, I expect logically one IP address and port 502 as enough (also you've set that correctly for sure in connection dialog). I see correct procedure as followed. Lets say you've read first device correctly and now you want go to next one (ID 247). I see correct procedure like this, we expect read one register for tests (LEN->1), MODE 0 (read):

1. set REQ -> false

2. set DISCONNECT -> true

3. set MB_Unit_ID to 247

4. set different destination register address (in case FC04 -> 38005 hope good remember or other as required)

5. set DISCONNECT -> false (connection will be established, check that or wait for a while)

6. set REQ->true (Client starts asking Server continuesly)

If all is ok then you will don't have errors and will have after that data inside your DB storage at first array element. If you want test next device with different ID tehn use same steps from point 1. This is procedure what must working. Via this steps you can also prepare good state machine for data collecting from different Slaves. I'm starting think from your PC Poll app what is functional and what parameters you have set there.