Omron SYSMAC CVM1 Series Operation Manual page 91

Mnemonic Code
OR LOAD
0000
00
0000
02
Logic Block Instructions in
Series
The above ladder diagram cannot be converted to mnemonic code using AND
and OR instructions alone. If an AND between CIO 000002 and the results of an
OR between CIO 000000 and CIO 000001 is attempted, the OR NOT between
CIO 000002 and CIO 000003 is lost and the OR NOT ends up being an OR NOT
between just CIO 000003 and the result of an AND between CIO 000002 and the
first OR. What we need is a way to do the OR (NOT)'s independently and then
combine the results.
To do this, we can use the LOAD or LOAD NOT instruction in the middle of an
instruction line. When LOAD or LOAD NOT is executed in this way, the current
execution condition is saved in special buffers and the logic process is begun
over. To combine the results of the current execution condition with that of a pre-
vious "unused" execution condition, an AND LOAD or an OR LOAD instruction is
used. Here "LOAD" refers to loading the last unused execution condition. An un-
used execution condition is produced by using the LOAD or LOAD NOT instruc-
tion for any but the first condition on an instruction line.
Analyzing the above ladder diagram in terms of mnemonic instructions, the
condition for CIO 000000 is a LOAD instruction and the condition below it is an
OR instruction between the status of CIO 000000 and that of CIO 000001. The
condition at CIO 000002 is another LOAD instruction and the condition below is
an OR NOT instruction, i.e., an OR between the status of CIO 000002 and the
inverse of the status of CIO 000003. To arrive at the execution condition for the
instruction at the right, the logical AND of the execution conditions resulting from
these two blocks would have to be taken. AND LOAD does this. The mnemonic
code for the ladder diagram is shown to the right of the diagram. The AND LOAD
instruction requires no operands of its own, because it operates on previously
determined execution conditions. Here too, dashes are used to indicate that no
operands needs designated or input.
The following diagram requires an OR LOAD instruction between the top logic
block and the bottom logic block. An ON execution condition would be produced
for the instruction at the right either when CIO 000000 is ON and CIO 000001 is
OFF or when CIO 000002 and CIO 000003 are both ON. The operation of and
mnemonic code for the OR LOAD instruction is exactly the same as those for a
AND LOAD instruction except that the current execution condition is ORed with
the last unused execution condition.
0000
01
0000
03
Naturally, some diagrams will require both AND LOAD and OR LOAD instruc-
tions.
To code diagrams with logic block instructions in series, the diagram must be
divided into logic blocks. Each block is coded using a LOAD instruction to code
the first condition, and then AND LOAD or OR LOAD is used to logically combine
the blocks. With both AND LOAD and OR LOAD there are two ways to achieve
this. One is to code the logic block instruction after the first two blocks and then
after each additional block. The other is to code all of the blocks to be combined,
starting each block with LOAD or LOAD NOT, and then to code the logic block
instructions which combine them. In this case, the instructions for the last pair of
blocks should be combined first, and then each preceding block should be com-
bined, working progressively back to the first block. Although either of these
methods will produce exactly the same result, the second method, that of coding
Address Instruction
Instruction Instruction
00000 LD
00001 AND
00002 LD
00003 AND NOT
00004 OR LD
Section 4-4
Operands
000000
000001
000002
000003
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