I'm testing out modbus TCP/IP for my home brewery, using Wago PFC200 as both slave and master. I'm using Wago library WagoAppPlcModbus.
Holding registers, input registers' and discrete inputs works fine, but when trying to write multiple coils, it doesn't work. Any idea what I'm doing wrong here?
Attached is a screenshot of my code. I tried both using bit mapping and without. If I change to FC05, and write only 1 coil at the time, it works fine. But I want to write all at the same time..
When you say it does not work, does nothing happen or do you get an error?
I have not used this function in codesys but from my past experience with Modbus I believe the coils need to be contiguous, which may be why yours is failing?
Have you tried using Write Registers (16) to do the job? Or is their data in-between you do not want to edit in the transaction?
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Thanks for your reply. I belive it is contiguous, I'm writing to adress 0 to 4. Or, do you mean something else?
Well, something is happening. If I on the client set adress 1,2,3 to true, only 1 is set to true on the server side.
On the client side, the data is array of word. But on the server side, the coils are array of bool. Holding register is array of word on server side. Can this be a problem?
Attached screenshot of how it looks at the server side.
If I am understanding what you are saying, then yes that would be your problem. I would create an array of bools on the client side for the transfer and try that. Or if client can't be changed then use words on server and unpack.
But I am not sure if you or I are mis interpreting but it sounds a bit jumbled. I don't know what you have control of, but, if you are turning on BITS in the server, you should write to BITS in the client with a Function 15. If you are writing to WORDS in the server, you should write to WORDS in the client with a Function 16.
Last edit: ben1 2024-11-17
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Thanks! As far as I can see, the client can only send words. And on the server side there are an array for each of the functions: bool for coil and discrete, word for holding and input registers.
I assume I can use holding register, then use bit mapping on the words instead of coils. But I really want to use the FC15/coils.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Yeah that is odd - sometimes you have to do what you have to do unfortunately.
Have you tried sending consecutive bits in the word instead - ie. instead of [0].0. [1].0, [2].0 etc, send [0].0,[0].1, [0].2 etc. ?
Hi there!
I'm testing out modbus TCP/IP for my home brewery, using Wago PFC200 as both slave and master. I'm using Wago library WagoAppPlcModbus.
Holding registers, input registers' and discrete inputs works fine, but when trying to write multiple coils, it doesn't work. Any idea what I'm doing wrong here?
Attached is a screenshot of my code. I tried both using bit mapping and without. If I change to FC05, and write only 1 coil at the time, it works fine. But I want to write all at the same time..
Any help is very appreciated :)
When you say it does not work, does nothing happen or do you get an error?
I have not used this function in codesys but from my past experience with Modbus I believe the coils need to be contiguous, which may be why yours is failing?
Have you tried using Write Registers (16) to do the job? Or is their data in-between you do not want to edit in the transaction?
Thanks for your reply. I belive it is contiguous, I'm writing to adress 0 to 4. Or, do you mean something else?
Well, something is happening. If I on the client set adress 1,2,3 to true, only 1 is set to true on the server side.
On the client side, the data is array of word. But on the server side, the coils are array of bool. Holding register is array of word on server side. Can this be a problem?
Attached screenshot of how it looks at the server side.
Last edit: garrian 2024-11-17
If I am understanding what you are saying, then yes that would be your problem. I would create an array of bools on the client side for the transfer and try that. Or if client can't be changed then use words on server and unpack.
But I am not sure if you or I are mis interpreting but it sounds a bit jumbled. I don't know what you have control of, but, if you are turning on BITS in the server, you should write to BITS in the client with a Function 15. If you are writing to WORDS in the server, you should write to WORDS in the client with a Function 16.
Last edit: ben1 2024-11-17
Thanks! As far as I can see, the client can only send words. And on the server side there are an array for each of the functions: bool for coil and discrete, word for holding and input registers.
I assume I can use holding register, then use bit mapping on the words instead of coils. But I really want to use the FC15/coils.
Yeah that is odd - sometimes you have to do what you have to do unfortunately.
Have you tried sending consecutive bits in the word instead - ie. instead of [0].0. [1].0, [2].0 etc, send [0].0,[0].1, [0].2 etc. ?
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