GE GFK0579B User Manual

Overriding an I/O circuit means changing its state or value in the PLC’s Override
Tables.  Overrides must be done from the PLC, with the remote  drop online.  Results
can be viewed on the programmer screen.  It cannot be done at the remote drop.

The override data is stored in the PLC, and survives loss of power in  the PLC.
However, if power is lost at the PLC but not at the remote drop, the Remote I/O
Scanner operates as it normally does if CPU communications are lost.  Outputs go to
their default state or hold their last state (as configured).  Once power is restored at the
PLC and CPU communications resume, the output overrides again take effect.

If a Logicmaster 90–70 programmer is communicating with the remote drop, circuits
can be toggled to alter the contents of the Remote I/O Scanner’s internal I/O tables.
Toggling circuits is only effective if inputs are not being received from an input module,
or if the Bus Controller is not sending CPU outputs to an output module.

If the system is operational and the remote drop is on–line, circuits must be toggled
from the PLC.  If the remote drop is off–line, it must be done locally.  Results can be
viewed on the programmer screen.

Once an input module has been inserted into the remote drop, the inputs scanned
from that module supersede any input data entered into the tables using Logicmaster
90–70.

Similarly, once output data starts being accepted for a module in the remote drop, it
supersedes any output data entered via Logicmaster 90–70.

Therefore, toggling I/O data while Logicmaster 90–70 is communicating with the PLC
is only effective temporarily, as real inputs and outputs will overwrite toggled inputs or
outputs as soon as they are received.

In short, forcing is the only method of that guarantees consistent I/O behaviour
regardless of power failures throughout the system, or communications interruptions.
If you want to check out a circuit at the remote drop, the simplest way is with a
Hand–held  Monitor, using force/unforce.