CODESYS CTUD

CTUD is a function block in the CODESYS Standard library that increments and decrements a given value. A rising edge on CU increments CV by one, and a rising edge on CD decrements CV by one. RESET sets CV to 0, LOAD sets CV to PV, QU is TRUE when CV >= PV, and QD is TRUE when CV = 0.

Source checked27/27 values · 2026-10-26

Specification

2 sources

Language	structured text
Code	CTUD
Group	Counter
Syntax	CTUDInst(CU := VarBOOL1, CD := VarBOOL2, RESET := VarBOOL3, LOAD := VarBOOL4, PV := VarWORD1);
Dialect	CODESYS

Parameters

Name	Data type	Description
CU	BOOL	Rising edge: Incrementing CV by one
CD	BOOL	Rising edge: Decrementing CV by one
RESET	BOOL	TRUE: Reset CV to 0
LOAD	BOOL	TRUE: Set CV to the start value PV
PV	WORD	Start value for decrementing / upper limit for incrementing
QU	BOOL	TRUE if CV >= PV
QD	BOOL	TRUE if CV = 0
CV	WORD	Current counter value

Study notes

The source notes that datatype WORD, used for PV in CODESYS, does not match the IEC standard, which defines PV as INT.