CTUD¶

Count up/down counter. Increments CV on rising edges of CU and decrements CV on rising edges of CD. Provides both an upper-limit output QU and a lower-limit output QD.

IEC 61131-3	Section 2.5.2.3.3
Support	Supported

Inputs

Name	Type	Description
`CU`	`BOOL`	Count-up input. Increments CV on each rising edge.
`CD`	`BOOL`	Count-down input. Decrements CV on each rising edge.
`R`	`BOOL`	Reset input. Resets CV to zero while TRUE.
`LD`	`BOOL`	Load input. Loads PV into CV while TRUE.
`PV`	`INT`	Preset value. The upper threshold for QU and the value loaded by LD.

Outputs

Name	Type	Description
`QU`	`BOOL`	TRUE when the current counter value CV is greater than or equal to PV.
`QD`	`BOOL`	TRUE when the current counter value CV is less than or equal to zero.
`CV`	`INT`	Current counter value.

Behavior¶

On each rising edge of CU, the counter value CV is incremented by one. On each rising edge of CD, CV is decremented by one. When R is TRUE, CV is reset to zero. When LD is TRUE, the preset value PV is loaded into CV. The output QU is TRUE when CV is greater than or equal to PV. The output QD is TRUE when CV is less than or equal to zero.

Typed variants CTUD_DINT, CTUD_LINT, CTUD_UDINT, and CTUD_ULINT use the corresponding integer type for PV and CV.

Example¶

This example counts up with CU held TRUE. After the first scan, CV is 1 which reaches PV, so at_max is TRUE.

Try it

Source

PROGRAM main
   VAR
      counter : CTUD;
      at_max : BOOL;
      at_min : BOOL;
      count : INT;
   END_VAR

   counter(CU := TRUE, CD := FALSE, R := FALSE, LD := FALSE, PV := 1,
           QU => at_max, QD => at_min, CV => count);
   (* After first scan: count = 1, at_max = TRUE, at_min = FALSE *)
END_PROGRAM

CTUD¶

Behavior¶

Example¶

See Also¶