Modbus with CompactLogix L32E using ModbusMaster.acd

[Marie1982]

Hi,

I'm trying to communicate between a CompactLogix L32E and a power transmitter using Modbus RTU. I use a 1761-NET-AIC. Has anyone ever used the sample file ModbusMaster.acd? I read another thread about this topic but it didn't answer my question.

I want to know how to manage de commands send to the slave. I know I can write up to 40 commands and that if I do, the PLC will execute them one after the other. What I want to do is verify if my command has successfully been sent. In the document (CIG-AP129A-EN-P page 32), they give four steps to do that. The second one is send the command to the Modbus slave... How do I control that? Just by putting ModCommand[].enable to 1?

Also, what happens if I have multiple read or write commands to do? If I do multiple reads, where do the data go? I see only one tag where the program sends data: Mod_Data_InpReg3. How do I manage that?

Thank you

Marie

 

[SBorn]

Setting the Mod_Commands[0].Enable bit to a 1 will trigger that command to start polling.

Mod_Commands[0].FunctionCode controls what modbus function code is used and will determine which array the data goes into.

If you set Mod_Commands[0].FunctionCode to a 3, it will perform a 4x register read and the data will be placed in Mod_DataHoldReg4 data array. The array element it ends up in will depend on what you have configured in Mod_Commands[0].AddressOffsetinMaster and Mod_Commands[0].StartingAddress. They are basically added together in the program so you have to be carefull on how those are set up.

 

[Marie1982]

Can u give me more explanation (examples) of where the data will end depending on what I put in the parameters?

 

[Marie1982]

Here is where u can find the manual of the power transmitter I'm trying to communicate with... My question is, am I in the 4xx or 3xx registers???

http://www.veris.com/product.asp?idMainCategory=45&idCategory=110&idProduct=129

(check the install manual)

Thanks.

 

[SBorn]

I can't remember exactly how the offset functioned, that was well over a year ago. The best of my memory was if you wanted to read 43051 and place it in data array 200 you needed the following parameters. Mod_Commands[4].StartingAddress = 3050, Mod_Commands[4].AddressOffsetinMaster = -2850. This might be off by a register so double check the data once you have it working.

 

[SBorn]

That manual is pretty interesting, it doesn't tell you what types the registers really are. The modbus protocol states that 3x registers are read only and 4x registers are read/write. I would try looking at the r/w column and use a 3x read (FC-4) for r and a 4x read (FC-3) for r/w registers.

 

[Marie1982]

Good advice thank you, I will try that as soon as I get the equipment.

 

[Contr_Conn]

Publication CIG-AP129A should be on your hard drive in a samples folder (v13+) or you can get it from the web http://literature.rockwellautomation.com/idc/groups/literature/documents/ap/cig-ap129_-en-p.pdf It will give you all details on how to use this application​

 

[Marie1982]

I have this document, but there is no explanation about how to use the code, only how to add it in the project. The only example doesn't answer my questions.

 

[rPraveenkum]

what is the modbus address you are trying to read/write post the address I will configure for you

 

[rPraveenkum]

I have this document, but there is no explanation about how to use the code, only how to add it in the project. The only example doesn't answer my questions.

Documentation explanation is good , you have to try the program & make feel of it

 

[rPraveenkum]

Program is build considering all aspects

 

[Marie1982]

Hi,

I have received all my components and am trying to communicate.

I am trying to read the system type of my power transmitter. It is located at the address 130. Since this address is a R/W, I guess it is in the 4xxxx registers.

Here is how I configured my Modbus command:

ModbusCommand[0].Enable = 0
ModbusCommand[0].EchoReceived = 0
ModbusCommand[0].ScanNumber = 0
ModbusCommand[0].OffsetAddress = 0
ModbusCommand[0].SlaveAddress = 1
ModbusCommand[0].FunctionCode = 4
ModbusCommand[0].StartingAddress = 130
ModbusCommand[0].NumberOfPoints = 1

When I enter those parameters, I have 0 both in
Mod_Data_InpReg3[130] and Mod_DataHoldReg4[130]

When I turn the enable bit to 1, EchoReceived turns to 1 and I get 100 in Mod_Data_InpReg3[130] and 0 in Mod_DataHoldReg4[130]. However, in the controller, I set the system type to 10, 40 and 42 and I got the same result.

How do I interpret that???

Thank you

 

[Marie1982]

I tried command code 3 and I got the 100 in the Mod_DataHoldReg4[130] register instead of the Mod_Data_InpReg3[130].

What is the difference between code 3 and code 4???

 

[SBorn]

Modbus function code 3 is a 4x register read and function code 4 is a 3x register read. Here is a brief list of common function codes.

Common Modbus function codesCodeDescription01Read coil status02Read input status03Read holding registers04Read input registers05Force single coil06Preset single register07Read exception status15Force multiple coils16Preset multiple registers17Report slave ID