Hello! I am using a Twido (Master) controller to communicate to 2 devices (Slaves). The slaves devices can only handle requests of 10 words at a time. It is required to read 45 word from each device. The 1st word of each device is called a Telegram and always returns a value of 900 when communicating. Currently, my ladder program uses a counter to increment through 5 read request per device. My problems is how do you determine when a device stops communicating with the master and which device? I am also looking for sample Echange and Message example code.

 

Hi!

Check with your local Schneider specialist if he can send to you the Modbus communication macro and the documentation.

We used it in an application where there's a Twido (master) communicating with a Modicon Quantum PLC (slave) and it's quite easy to use.

 

I can Email you an example application. There is an explanation of the EXCH / Message function in the Twido software manual, but its not as clear as it should be.

Email me

[email protected]

 

use the EXCH instruction to send your read request
and verify that the request has ended well by testing
the relevant MSGx.D bit (1: request ended, 0 request under way) and MSGx.E bit (0 : no error, 1 last request ended on error) your application could be (in IL) :

xxx (fill the comm table)
EXCH1(%MWx:y) (* first *)
[%MWz := 1] (* message counter *)

LD MSG1.D (* request ended *)
ANDN MSG1.E (* no error *)
AND [ %MWz < max_counter_value ]
xxxx (* modify the comm table for next request *)
yyyy (* process the received values *)
EXCH MSG1(%MWx:y)(* send next request *)

LD MSG1.D (* request ended *)
AND MSG1.E (* error *)
yyyy (* do what you need to treat the error *)

... and so on