Gould Modicon PLC 884 with ModBus

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Thread Starter

Ansari

I am communicating Gould Modicon PLC 884 using Modbus RTU protocol. I am facing following difficulties in using modbus function codes:

(1) when i am forcing contact of B805 Output module using Modbus function code, the output forces to ON but reset automatically after some moments. Can the output be hold or latched until we send function code for the contact to force OFF?

(2) Is it possible to force the input contacts of B804 modules using modbus function code for simulation purpose?

(3) I want to add one more B804 module, is it possible to configure the 884 controller using Modbus function code for this addition?

(4) which function code is used for reading and writing the logic program from/to the 884 controller and what will be the querry for this purpose?

(5) How we can read or write the internal memory contacts (not external I/O)? which function is used for this purpose?

I will be very thankful, if any body help me for solving my above problems.
 
Thank you Mr. Wassim for reply. Actually I am using Visual Basic and Modbus function codes for creating HMI to Gould Modicon PLC 884 System. For this purpose I want to know the details about Modbus function codes in respect of mentioned points
 
L

Lynn August Linse

> (1) when i am forcing contact of B805 Output module using Modbus function
> code, the output forces to ON but reset automatically after some moments. Can
> the output be hold or latched until we send function code for the contact to force OFF?

This probably means that output B805 is driven by an active rung - so you set it high and the next PLC cycle it returns to the "correct" state as the run is updated.

So you are fighting against the PLC, which will always win!

You need to remove coil B805 from any of the ladder logic. If you are trying to temporarily 'force' a coil for testing, then you need to use a different method - a non-standard Modbus function.
 
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