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Chapter 10: Function Blocks LogicPro User’s Guide

118 Watlow Anafaze Doc.# 28002-00 Rev 3.00

Figure 10.3 Counter Down Function Block

Inputs

CD is the Counter Down enable bit. As long as the reset bit is

False, each False to True transition of this bit decrements the

current value until the current value equals zero. In a program

using Ladder logic, the value of CD is determined by the

Boolean evaluation of elements placed between the left power

rail and CD in the function block. In

FBD programs, the value

of CD is determined by the Variable connected to CD. If no

contacts are placed on the rung before or Variable attached to

CD, the value of CD is always True, but a transition never

occurs.

LD is the Counter Down load bit. When this bit is True, the

current value is set to the preset value and the output bit is

disabled. In Ladder Diagram programs, the value of LD is

determined by the Boolean evaluation of elements placed

between the left power rail and LD. In

FBD programs, the

value of LD is determined by the Variable connected to LD.

PV is the Counter Down preset value. In Ladder logic, assign

this input a symbolic name or constant value in the Assign

Function Block Symbolic Input/Output dialog box. In

FBD, assign a variable to this input in the Variable

Assignment dialog box. The range of values this Variable

can assume is from 1 to 32,767 for INT type Variables and 1

to 2,147,483,647 for LONG type Variables. If this Variable is

assigned a value out of these ranges, unpredictable results will

occur.

Outputs

Q is the Counter Down output bit. This bit is enabled and

passes power when the current value is equal to zero. Prior to

an initial loading of the preset value, Q is not enabled even

though the current value is set to zero.

CV is the Counter Down current value. In Ladder logic, assign

this output a symbolic name or constant value in the Assign

Function Block Symbolic Input/Output dialog box. In

FBD, assign a variable to this output in the Variable

Assignment dialog box. The value of this Variable

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Watlow LogicPro Bedienungsanleitung Seite 134