Watlow LogicPro - Manual (Page 135)

LogicPro User’s Guide Chapter 10: Function Blocks
Doc.# 28002-00 Rev 3.00 Watlow Anafaze 119
decrements by one every time a False to True transition of the
counter down enable bit occurs until the current value equals
zero. The current value retains this value until the reset bit is
True. Prior to an initial loading of the preset value, CV has a
value of zero.
Counter Up Down (CTUD)
The Counter Up Down function block, shown in Figure 10.4,
is a combination of the counter up and counter down function
blocks.
CTUD increments the integer current value (CV) for every
False to True transition of the counter up enable bit (CU), and
decrements the current value for every False to True transition
of the counter down enable bit (CD). The current value
continues to increment or decrement depending on which
enable bit becomes True until either the integer preset value
(PV) or zero is reached. At this point, the up output bit (QU) is
enabled if the current value equals the preset value, or the
down output bit (QD) is enabled if the current value equals
zero.
The output bit remains enabled until reset by a True condition
of the (R) or (LD) bit respectively. When the reset bit (R) is
True, the current value resets and remains at zero. When the
load bit (LD) is True, the current value resets and remains at
the preset value.
Figure 10.4 Counter Up Down Function Block
Inputs
CU is the Counter Up enable bit. As long as the reset bit is
False, each False to True transition of this bit increments the
current value until the current value equals the preset value. In
a program using Ladder logic, the value of CU is determined
by the Boolean evaluation of elements placed between the left
power rail and CU in the function block. In
FBD programs, the