UT_IO_FORCE_RUN — One IO force slot (function)

The engine of one commissioning force slot, shared by
UT_IO_MAP_IN and UT_IO_MAP_OUT. Not for your
programs: the IO maps call it, once per slot per scan. This page explains how a
force starts, runs and ends, for the HMI's force page.

It is a function, not a function block. The slot (UT_IO_FORCE, described on
UT_IO_MAP_IN) keeps all its state.

Pins

IF UT_IO_FORCE_RUN(S := Force[j], Where := where, Permit := ForcePermit, Release := ReleaseAll,
                   Elapsed := tStep, ForceTime := ft) THEN
  (* put the forced value on the slot's channel *)
END_IF;

The slot's status

There are no status codes: the maps report forcing in their own status (Warning: IO forced, forcedCount, forceLeft).

How it works

1. Commands act once. cmdForce and cmdRelease act on their rising edge and
   are cleared every scan. The slot remembers the last value it read
   (forceSeen, releaseSeen), so a command held on (a Modbus coil, a debugger
   force) acts once, and acts again only after it has been FALSE for a scan.
2. Release first. cmdRelease or Release ends a force at once (state
   UNUSED). While Release is TRUE, a cmdForce is refused and is not kept for
   later.
3. Start. cmdForce starts a force with timeLeft = ForceTime, if Where is OK
   and Permit is TRUE. Otherwise it is refused, and state says why. cmdForce
   on a slot that is already forcing starts its time again.
4. Running. Each scan timeLeft goes down by Elapsed. If ForceTime has been
   made shorter, timeLeft is cut to it at once. At 0 the force ends (state
   UNUSED).
5. Lost on the way. A force ends at once if Where stops being OK (the address
   was changed to one that does not exist) or Permit drops (state says which).
   The slot's address itself is not checked here: the map looks up the channel from
   the slot's address every scan, so a new address that exists moves the force.
6. The function does not look at the slot's kind: the input map handles DI and AI
   slots (and clears NONE ones), the output map DO and AO slots.

Nothing is kept over a power cut. Never declare the force slots RETAIN.