UT_SETTING_CHECK — Check a setting before it is used

An HMI or SCADA user can type anything: a stop level above the start level, a
negative time, a number with a slipped decimal point. UT_SETTING_CHECK takes a
written setting only if it is sensible, and otherwise keeps the old one and says
why, as a UT_FAULT code the HMI turns into its own words (not below related).

UT_SETTING_ARRAY does the same for a whole list of settings in one block (see
below).

Pins (UT_SETTING_CHECK)

How it works

New is checked each time it changes, or on a rising edge of Written:

Passed: Value := New, RefusedWhy UT_F_NONE. Refused: Value keeps its old value
and RefusedWhy says why. The HMI knows which setting it wrote, so it can show its
own words, e.g. "L refused: not below H".

• A master that writes the same refused value every poll is refused once (the value
  hasn't changed). After fixing the related setting, write the value again, or
  pulse Written.
• Nothing is checked on the first scan after a power cut or PLC start: New is
  only read. A master variable that comes back 0 never overwrites a setting kept in
  a RETAIN record.
• The HMI shows Value (the setting in use) and writes New.
• For two related settings use two blocks, each with the other as its limit:
  L with Below := H, H with Above := L.

LChk(New := HMI_LevelL, MinValue := 0.0, MaxValue := 5.0, Below := Cfg.levelH,
     Value := Cfg.levelL);
HChk(New := HMI_LevelH, MinValue := 0.0, MaxValue := 5.0, Above := Cfg.levelL,
     Value := Cfg.levelH);
HRefused := HChk.RefusedWhy;     (* UT_F_NOT_ABOVE: H not above L *)

UT_SETTING_ARRAY — a list of settings

Record UT_SETTING (one item)

• The checks and RefusedWhy codes are UT_SETTING_CHECK's. A position outside the array, or
  the item's own position, means no check.
• Items are checked in array order. When two related items change in the same
  scan, the later one is checked against the earlier one's new value; the earlier
  one against the later one's old value (it may then need cmdCheck).
• Nothing is checked on the first scan after power-up. Declare the array RETAIN
  to keep the settings over a power cut.

(* Levels[1] = L, Levels[2] = H: L.below := 2, H.above := 1 *)
LevelSettings(Items := Levels);
Station.stage[1].stop := Levels[1].value;
Station.stage[1].start := Levels[2].value;