Watlow LogicPro - Manual (Page 152)

Chapter 10: Function Blocks LogicPro User’s Guide
136 Watlow Anafaze Doc.# 28002-00 Rev 3.00
Inputs
LD is the FIFO load bit. As long as the clear bit is False, each
False to True transition of this bit loads the input Variable
value into the stack until the count value equals the size value.
In a program using Ladder logic, 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 True, but a transition never occurs. This bit has the
lowest evaluation priority of the input bits in this function
block.
UNLD is the FIFO unload bit. As long as the clear bit is False
and the count value is not zero, each False to True transition
of this bit unloads the oldest integer in the stack to the output
Variable. In a Ladder Diagram program, the value of UNLD is
determined by the Boolean evaluation of elements placed
between the left power rail and UNLD in the function block. In
FBD programs, the value of UNLD is determined by the
Variable connected to UNLD. If no contacts are placed on the
rung before UNLD, the value of UNLD is always False. This bit
has higher evaluation priority than the LD bit in this function
block.
CLR is the FIFO clear bit. When this bit is True, the stack is
cleared of any values and the count Variable is set to zero. In
a Ladder Diagram program, the value of CLR is determined by
the Boolean evaluation of elements placed between the left
power rail and CLR in the function block. In FBD programs,
the value of CLR is determined by the Variable connected to
EN. If no contacts are placed on the rung before CLR, the value
of CLR is always False. This bit takes the highest evaluation
priority of the input bits in this function block.
INP is the FIFO input Variable. 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 value of this Variable is placed
in the stack at the location of the count Variable. The range
values this Variable can assume is from -32,768 to 32,767,
including 0. If this Variable is assigned a value out of these
ranges, unpredictable results will occur.
SIZE is the FIFO size Variable. This value assigned to this
Variable determines the size of the stack. For this reason,
assign a constant value and do not change this value online.