CODESYS CTD

CTD is a standard function block that decrements a counter value. A rising edge on the CD input reduces the current counter value CV by one, and LOAD set to TRUE loads CV with the start value PV. The output Q is TRUE when CV equals zero.

Source checked18/18 values · 2026-10-26

Specification

2 sources

Language	structured text
Code	CTD
Group	Counter
Syntax	CTDInst(CD:=VarBOOL1, LOAD:=VarBOOL2, PV:=VarWORD1);
Dialect	CODESYS

Parameters

Name	Data type	Description
CD	BOOL	Rising edge: decrementing CV by one
LOAD	BOOL	TRUE: Set CV to the start value PV
PV	WORD	Start value for decrementing
Q	BOOL	TRUE if CV = 0
CV	WORD	Current counter value

Study notes

The block must be declared as an instance before use, e.g. CTDInst : CTD;
Results are read from the instance after the call, e.g. VarBOOL3 := CTDInst.Q; and VarWORD2 := CTDInst.CV;
Listed under the Counter group of the Standard library.