more than one 'job' per modbus connection?

Hi All,

If I want to have more than one 'job' per modbus connection, what is the best way of doing it ?

Say I want two jobs on connection ID number 1.

Do I have two instances of MB_Client and activate "REQ' on the first instance and just EN on the next instance or do I need to activate REQ for both jobs.

I would have thought activating REQ for both instances would mean sending a connection request to an already 'open' connection'.....or does the block need a REQ to send the data even if the connection is already established ?

Cheers !

------------------------------------------------------------------------------------------
Split from Connecting PLC 1500 to Modbus TCPIP in TIA Portal.

Hi,
Not all Modbus servers support jobs in parallel very well.
So best use a sequence (next job when the previous is done).  

The MC_client holds in its instance DB information about the status of the connection.
So, over one and the same connection, you best keep using the same instance DB (or multiIsnstace).
To keep the connection open between jobs, you parameterized "disconnect" as false.

For each new job, you can have a call of MB_Client with that Instance and the parameters like the registers you want to read/write  (MB_MODE, MB_ADDRESS, length, Data_pointer) and you trigger REQ once (pulse).
But you execute only one at a time by using the EN(enable) input.  
When the DONE comes (or Error, or Timeout), you enable the next job and disable all other calls.

See a suggested solution as annex.
Not fully tested, just the basic steps I would take.