CTD: Down Counter Function Block

Introduction

The CTD function block decrements a count for each rising edge until the count reaches zero.

Parameters

Parameter	Type	Direction	Description
CD	BOOL R_EDGE	Input	A rising edge decrements the counter value CV by 1.
LD	BOOL	Input	Resets the output Q and the counter value CV.
PV	INT	Input	The counter limit value.
Q	BOOL	Output	Set to true when the counter value CV reaches PV.
CV	INT	Input	The current counter value.

The Up Counter is logically equivalent to:

Function_Block CTD
        Var_Input CD : BOOL R_EDGE; LD : BOOL; PV : INT; End_Var
        Var_Output Q : BOOL; CV : INT; End_Var

        IF LD THEN
            CV := PV;
        ELSEIF CU AND (CV > 0)
            CV := CV - 1;
        END_IF;

        Q := (CV <= 0);
    End_Function_Block

Standards Compliance

IEC 61131-3 Second Edition: Table 36.2a.

IEC 61131-3 Third Edition: Table 44.2a.

Further Information

Standard Function Blocks

To learn about other standard function blocks.

Elementary Data Types

To learn about the different types supported by Fernhill SCADA.

Common Elements

To learn about other IEC 61131-3 Common Elements.

Glossary

For the meaning of terms used in Fernhill SCADA.