Watlow LogicPro - Manual (Page 136)

Chapter 10: Function Blocks LogicPro User’s Guide
120 Watlow Anafaze Doc.# 28002-00 Rev 3.00
value of CU is determined by the Variable connected to CU. If
no contacts are placed on the rung before CU, the value of CU
is always True, but a transition never occurs. This bit has
higher evaluation priority than the CD bit in this function
block.
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 Ladder
Diagram program, 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 CD, the default value of
CD is True. This bit has the lowest evaluation priority of the
input bits in this function block.
R is the Counter Up reset bit. When this bit is True, the current
value is set to zero and the QD output bit is disabled. In a
Ladder Diagram program, the value of R is determined by the
Boolean evaluation of elements placed between the left power
rail and R in the function block. In
FBD programs, the value of
R is determined by the Variable connected to R. If no contacts
are placed on the rung before R, the value of R is always False.
This bit has the highest evaluation priority of the input bits in
this function block.
LD is the Counter Down load bit. When this bit is True, the
current value is set to the preset value and the QU output bit is
disabled. In a Ladder Diagram program, the value of LD is
determined by the Boolean evaluation of elements placed
between the left power rail and LD in the function block. In
FBD programs, the value of LD is determined by the Variable
connected to LD. If no contacts are placed on the rung before
LD, the value of LD is always False. This bit has higher
evaluation priority than the CD bit in this function block.
PV is the Counter Up 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.