Once again on XXMIT Instruction, i am using CPU 434 12 and concept 2.6, Do i have to purchase XXMIT Loadable (Instruction) as it was not there with other PLCs of Quantum Series. if yes then how much it will cost......

Furthermore i am planning to use modbus ethernet gateway which will avail the facility to communicate with out XXMIT. In this case also (I think) I have got three options for PLC to Gateway communication:
1) using MSTR Instruction
2) using ethernet I/O Scanner
3) using CREAD_REG CWRITE_REG

am i right.......?
Waiting for a detailed answer.
Thank you in advance.

 

XXMIT and XMIT are there for free - just paste in the DFB.

Your PLC/Gateway options are correct however you should find out how many concurrent TCP sockets can be used concurrently by the bridge. The reason is that if you use the IO scanner which is by far the easiest then you have no control over when a messgae gets sent (or flow control). The IO scanner just blasts out sockets (1 for each entry) tot he device. If for example you are using the 174 CEV bridge, it only support 8 concurrent sockets otherwise the 9th gets lost. If you are using the Powerlogix EGX bridge it only supports 10 sockets over the 2 serial ports. So if you have any more devices then this (allow yourself 1 socket for diagnostics/config) then you will need to mutiplex in code using MSTR OR upgrade to Unity which has enable/disable for each entry in the IO scanner so you multiplex via this. Either way - it takes some code management.

When you use MSTR note that there can only be 4 concurrent MSTR blocks used in the program. Schneider actually told me on Modbus TCP you could use 16 but in testing we found this was wrong. To achive this we had to write a DFB to control 4 MSTR blocks for maximum throughput based on some queuing logic on retry counts (comms barometer), polling rates, time since last retry etc....

Regards

Brad Stemp
Activ8 Engineering Pty Ltd
[email protected]

 

You can get extra connections if you reset the Watchdog in the segment scheduler in between blocks of 4 MSTR calls but do this at your own risk. I think it is safer to do as you have done and carefully schedule the MSTR comms. The MSTR is more controllable than the CREAD_REG which runs flat out and can overload some networks.