The DISA loadable allows the ladder diagram of a Quantum or Compact PLC to find and annunciate disable states as they occur. The instruction logs the quantity and reference number of the disabled coils and inputs into simple data tables, enabling the controller to annunciate this information locally.
For further details refer to the DISA Installation and User Guide (3100319901) available on http://www.modicon.com.
> I want to read the forced coil status from Modicon PLC.I have scanned through all the modbus commands available but no command to know above.<
Use the Read Coil command (01H) for reading coil status. To force a coil use the Force Coil commands (05H, 0FH). Note that according to the Modbus standard documentation, a forced coil will only remain in the forced state until the next time the ladder logic is solved. This may only be 10-20ms or less. The state that you will read with the 01H command will likely be the non-forced, and most current state.
I think you mean you want to detect if/which inputs are being forced 1/0 and which are free-moving inputs?
This is done by Modicon using some vendor-specific commands not included in any of the public specs. All I can suggest is a painful reverse engineer of Modicon software seeing this - create a simple rung with 1 status input, force it to zero. Capture the traffic and I'd guess the bulk of it would be the info you want repeated every second. Then unforce it, and look again. Hopefully the only significant change in this steady 1 second polling is the force-status you desire.
