Sending slave recipe via Modbus

[ofer.yishai]

Hello,

 

I would like to send a program (recipe) to external process controller/programmer (e.g. Eurotherm 3504) via Modbus IP or RS-485. each parameter has its Modbus address and value in a table.

 

The thing is that parameters should be written only once and in a certain order, if the order is not kept then the receiving instrument may not accept some values.

 

 I have a few questions:

 

1. Is the execution order of the remote slave configuration table is strictly kept? (Like if all rows has the same period, and all use the same active bit )

 

2. What is the way to write each address only once (and not repetitively every period)?

 

3. I was thinking to use different "Active" bits configured in each row in a sequence. How can I get a feedback (like "function in progress" falls in Vision series) that will aid to advance the sequencer? (also to reset the active bit in duty and to set the next one). Would it be advised to go this way?

 

Any advice will be appreciated,

 

Thanks

 

[Ofir]

Hi,

 

The best way in the case is to use Aperiodic.

Select MODBUS Master in the Solution explorer and then on the properties window you should be able to select between Periodic and Aperiodic.

Once Aperiodic selected you will see in the table that the columns of the periods doesnt exist anymore.

Now you can choose from the Ladder toolbox COM:Modbus --> MODBUS Aperiodic Trigger and link the commnad you wish to send.

Please make sure set a delay between activations of different MODBUS Aperiodic Trigger.

[ofer.yishai]

Thanks Ofir for your advice. I find it very helpful.

 

There are other reading tasks for the Modbus Master configuration, from this and other slaves. For this tasks the advantage of periodic setting is worth a fortune.  If changing from Periodic to Aperiodic then I guess that i will have to manage ALL slaves reading and writings by ladder..or is there another way?

Do you think Modbus advanced function can be use for writing only, and readings with periodic function? if yes, can you provide some instructions or sample application?

 

I would suggest to put the Periodic/Aperiodic setting for each slave configuration, this way the system will be more flexible. any sens?

 

Ofer