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[on:]

I am starting a project to build a Modbus RTU slave using a MAX485 and an UNO. I have seen all the projects available on the web but all seem to be outdated. Any information or code to get started would be appreciated

[Reply #1 on:]

Hi
I hope this tutorial http://www.biemmeitalia.net/blog/android-touchscreen-communicates-with-arduino-using-modbus-rs485 might help you.

elle

[Reply #2 on:]

Thanks for the information the project looks great

I have tried to compile your code and the original SImpleModbusSlave example and both give the same error

SimpleModbusSlaveExample.ino: In function 'void setup()':
SimpleModbusSlaveExample:85: error: 'modbus_configure' was not declared in this scope
SimpleModbusSlaveExample.ino: In function 'void loop()':
SimpleModbusSlaveExample:95: error: 'modbus_update' was not declared in this scope

There is some information that this is related to the version of Arduino and I ahve compiled in 1.01 and the error is the same

Any ideas?

[Reply #3 on:]

looks like you dont have the modbus rtu library installed.
the code is making refference to it but its not there.
find your arduinos program directory - look for a folder called libraries and see if its in there, if not do a google search for it, download it and add it to this folder - restart the arduino application.
and it should be ok.

[Reply #4 on:]

right
You'll find the modbus library used in the project at http://code.google.com/p/simple-modbus/.

elle

[Reply #5 on:]

Thanks for the help I am making some progress. I have got the slave communicating with a master using the SimpleSlaveModbus example. When I try to use the code from the Android/Arduino project there is an error on line 34. I have tried to find the problem from the reference but no solution as yet.

sketch_feb09a.ino: In function 'void setup()':
sketch_feb09a:34: error: expected `;' before 'pinMode'
sketch_feb09a:34: error: expected `)' before ';' token
sketch_feb09a.ino: At global scope:
sketch_feb09a:38: error: expected constructor, destructor, or type conversion before '(' token
sketch_feb09a:39: error: expected constructor, destructor, or type conversion before '(' token
sketch_feb09a:40: error: expected constructor, destructor, or type conversion before '(' token
sketch_feb09a:41: error: expected constructor, destructor, or type conversion before '(' token
sketch_feb09a:44: error: expected constructor, destructor, or type conversion before '(' token
sketch_feb09a:47: error: expected constructor, destructor, or type conversion before '(' token
sketch_feb09a:50: error: expected unqualified-id before 'for'
sketch_feb09a:50: error: expected constructor, destructor, or type conversion before '<' token
sketch_feb09a:50: error: expected constructor, destructor, or type conversion before '++' token
sketch_feb09a:53: error: expected declaration before '}' token

[Reply #6 on:]

Sorry mtoko, there was a minor issue with the website so that the source code was not correctly displayed. Now it should work.
Thank you for point it out!

Remember: the two parts of the code (the one with the setup and the other with loop function) belong to the same Arduino sketch, so they must be together

elle

[Reply #7 on:]

Use this library. It is so simple and works.

http://code.google.com/p/arduino-modbus-slave/downloads/detail?name=MODBUS.zip&can=2&q=

[Reply #8 on:]

Hi,

I've build a C code for Modbus TCP/RTU included in an open source project called Souliss, you can get the code from there.

If you need any help to get it out, just ask.

Regards,
Dario.