How to run Modbus TCP in real time using Simulink?

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Bartosz Soltowski
Bartosz Soltowski 2021-8-30
编辑： Van Tu Duong 2024-5-9
Hi,
I have a Matlab script to communicate with my relay using Modbus TCP. The script was generated using Modbus Explorer in Matlab.
The code works well. It turns on/off my relay according to specified conditions as well as reads its status.
I am now trying to execute Matlab code from my Simulink model. I imported Matlab Function block which includes Matlab code (generated before) to control the relay. When I click Run button, I am getting error below:
Cannot write 'double' data to the buffer. The input data have to be 'uint8' type. Function 'MATLAB Function' (#24.1132.1168), line 31, column 1: "write(m, 'coils', 1000, 1, serverId)"
I tried to change names of my variables (as someone suggested that this could be the issue), I also changed all data types but I could not fix it.
I can't understand why am I getting this error if the same code executed in Matlab works fine?
I would be really grateful for your help!

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回答（4 个）

Bazarov
Bazarov 2022-7-11
Hi,
I have the same problem. Can anybody help?
Akshay Jankee
Akshay Jankee 2023-2-2
Hi Bartosz and Bazarov,
I also need to do something similar. Have you managed to sort out this issue?
Best regards,
Akshay
TryHarder
TryHarder 2023-11-22
编辑：TryHarder 2023-11-22
Hi everyone,
I have the same issue when I add a constant as an input of my function.
FWIW, the following function works nice from a MatLab function in Simulink :
function dataWrite = dataWrite
modbustype = 'tcpip';
modbusserver = '192.168.0.80';
modbusport = 502 ;
m = modbus(modbustype, modbusserver,modbusport);
write(m,'coils', 1, 1) ;
dataWrite = 1;
But with a constant as an input (activated with a button (on-off)), it did not work and I get the same error message...
function dataWrite = dataWrite(input)
modbustype = 'tcpip';
modbusserver = '192.168.0.80';
modbusport = 502 ;
value = uint8(input) % also test with double(input) or without cast in ordre to debug...
m = modbus(modbustype, modbusserver,modbusport);
write(m,'coils', 1, value) ;
dataWrite = value ; % To a display bloc
If someone had faced the same issue, I am all ears
Thx
Van Tu Duong
Van Tu Duong 2024-5-9
编辑：Van Tu Duong 2024-5-9
This can be fixed by using coder.extrinsic. You can try this code:
function dataWrite = dataWrite(input)
modbustype = 'tcpip';
modbusserver = '192.168.0.80';
modbusport = 502 ;
coder.extrinsic('modbus');
coder.extrinsic('write');
m = modbus(modbustype, modbusserver,modbusport);
write(m,'coils', 1, input) ;
dataWrite = input;

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