Selection functions

SEL — binary select

SEL(G: BOOL, IN0: ANY, IN1: ANY): ANY — returns IN0 when G = FALSE, IN1 when G = TRUE. Both IN0 and IN1 must be the same type; the result has that type.

iResult := SEL(xMode, iValueA, iValueB);
(* iResult := iValueA when xMode is FALSE
   iResult := iValueB when xMode is TRUE *)

Equivalent to:

IF xMode THEN iResult := iValueB; ELSE iResult := iValueA; END_IF;

MUX — multi-way select

MUX(K: ANY_INT, IN0: ANY, IN1: ANY, IN2: ANY, ...): ANY — returns IN<K>. The number of IN arguments is variable and must cover the range of K. Out-of-range K is implementation- defined (matiec returns IN0).

iResult := MUX(iSelector, 10, 20, 30, 40);
(* iResult := 10 when iSelector=0, 20 when 1, etc. *)

MUX is essentially a poor-man’s CASE-as-expression — useful when you need to compute one of N values inside a larger expression where CASE (a statement) wouldn’t fit.

MIN, MAX — extremum of variadic args

MIN(IN1: ANY_NUM, IN2: ANY_NUM, ...): ANY_NUM — smallest of all inputs. All arguments must share a type.

MAX(IN1: ANY_NUM, IN2: ANY_NUM, ...): ANY_NUM — largest.

iSmallest := MIN(iA, iB, iC, iD);
rPeak     := MAX(rSensor1, rSensor2, rSensor3);

For BOOLs, use AND (boolean MIN: TRUE if ALL are TRUE) and OR (boolean MAX: TRUE if ANY is TRUE) — see llm_signals.

LIMIT — clamp to a range

LIMIT(MN: ANY_NUM, IN: ANY_NUM, MX: ANY_NUM): ANY_NUM — returns IN clamped to [MN, MX]:

result := MAX(MN, MIN(IN, MX))

(* clamp a sensor reading to the valid PT100 range *)
rTemperature := LIMIT(MN := -50.0,
                      IN := rRawTemp,
                      MX := 200.0);

(* clamp an INT step counter *)
iStep := LIMIT(0, iStepRaw, 5);

LIMIT is the standard idiom for “saturate at boundaries” — prefer it over hand-written IF cascades when the bounds are known.

IEC reference

IEC 61131-3 third edition (2013), Annex F.2.4 — “Selection functions” Table F.8.

matiec conformance

All five functions implemented per the standard. The variadic forms (MUX, MIN, MAX with N inputs) accept up to 32 inputs in matiec — the standard doesn’t bound this.

LIMIT’s behaviour when MN > MX is undefined per the spec; matiec returns IN unchanged. Validate the bounds yourself when they’re computed at runtime.