Automationdirect.com DL06 - Page 169

DL06 Micro PLC User Manual, 3rd Edition, Rev. E
5-8
Chapter 5: Standard RLL Instructions
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Comparative Boolean
Some PLC manufacturers make it really difficult to do a simple comparison of two numbers.
Some of them require you to move the data all over the place before you can actually perform
the comparison. The DL06 Micro PLCs provide Comparative Boolean instructions that allow
you to quickly and easily solve this problem. The Comparative Boolean provides evaluation of
two BCD values using boolean contacts. The valid evaluations are: equal to, not equal to, equal
to or greater than, and less than.
In the example, when the BCD value in V-memory
location V1400 is equal to the constant value 1234, Y3
will energize.
Boolean Stack
There are limits to how many elements you can include in a rung. This is because the DL06
PLCs use an 8-level boolean stack to evaluate the various logic elements. The boolean stack is
a temporary storage area that solves the logic for the rung. Each time the program encounters a
STR instruction, the instruction is placed on the top of the stack. Any other STR instructions
already on the boolean stack are pushed down a level. The ANDSTR, and ORSTR instructions
combine levels of the boolean stack when they are encountered. An error will occur during
program compilation if the CPU encounters a rung that uses more than the eight levels of the
boolean stack.
The following example shows how the boolean stack is used to solve boolean logic.
X1 or (X2 AND X3)
STR X0 STR X1 STR X2
1
STR X0
2
3
4
1
STR X1
2
STR X0
3
4
1
STR X2
STR X1
2
3
STR X0
4
AND X3
1 X2 AND X3
2
STR X1
3 STR X0
4
ORSTR
1
2
STR X0
3
OUT
Y0
X0
X1
X2 X3
X4
X5
STR
OR
AND
ORSTR
ANDSTR
Output
STR
STR
AND
X4 AND {X1 or (X2 AND X3)}
AND X4
1
2 STR X0
3
NOT X5 OR X4 AND {X1 OR (X2 AND X3)}
STR X0
ORNOT X5
1
2
3
ANDSTR
XO AND (NOT X5 or X4) AND {X1 or (X2 AND X3)}
1
2
3
Y3
OUT
V1400
K1234