Logic Block Instructions - Omron SYSMAC C20P Operation Manual

The Ladder Diagram
OR and OR NOT
Combining AND and OR
Instructions
4–3–3

Logic Block Instructions

Actually, AND instructions can be considered individually in series, each of
which would take the logical AND between the execution condition (i.e., the
sum of all conditions up to that point) and the status of the AND instruction's
operand bit. If both of these were ON, an ON execution condition would be
produced for the next instruction. The execution condition for the first AND
instruction in a series would be the first condition on the instruction line.
Each AND NOT instruction in a series would take the logical AND between
its execution condition and the inverse of its operand bit.
When two or more conditions lie on separate instruction lines running in par-
allel and then joining together, the first condition corresponds to a Load or
Load NOT instruction; the rest of the conditions correspond to OR or OR
NOT instructions. The following example shows three conditions which corre-
spond in order from the top to a Load NOT, an OR NOT, and an OR instruc-
tion.
0000
0100
HR 000
The instruction at the right would have an ON execution condition when any
one of the three conditions was ON, i.e., when IR 0000 was OFF, when IR
0100 was OFF, or when HR 000 was ON.
OR and OR NOT instructions can also be considered individually, each tak-
ing the logical OR between its execution condition and the status of the OR
instruction's operand bit. If either one of these were ON, an ON execution
condition would be produced for the next instruction.
When AND and OR instructions are combined in more complicated dia-
grams, they can sometimes be considered individually, with each instruction
performing a logic operation on the execution condition and the status of the
operand bit. The following is one example.
0000 0001 0002 0003
0200
Here, an AND is taken between the status of 0000 and that of 0001 to deter-
mine the execution condition for an OR with the status of 0200. The result of
this operation determines the execution condition for an AND with the status
of 0002, which in turn determines the execution condition for an AND with the
inverse of the status of 0003. In more complicated diagrams, however, it is
necessary to consider logic blocks before an execution condition can be de-
termined for the final instruction, and that's where AND Load and OR Load
instructions are used.
Logic block instructions do not correspond to specific conditions on the lad-
der diagram; rather, they describe relationships between logic blocks. The
Section 4–3
Instruction
Instruction
33