Omron SRM1 - PROGRAMING 02-2001, Руководство по программированию

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6-3 Section Basic Ladder Diagrams
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The two logic blocks are indicated by dotted lines. Studying this example shows
that an ON execution condition will be produced when: either of the conditions in
the left logic block is ON (i.e., when either IR 00000 or IR 00001 is ON),
and
when either of the conditions in the right logic block is ON (i.e., when either IR
00002 is ON or IR 00003 is OFF).
The above ladder diagram cannot, however, be converted to mnemonic code
using AND and OR instructions alone. If an AND between IR 00002 and the re-
sults of an OR between IR 00000 and IR 00001 is attempted, the OR NOT be-
tween IR 00002 and IR 00003 is lost and the OR NOT ends up being an OR NOT
between just IR 00003 and the result of an AND between IR 00002 and the first
OR. What we need is a way to do the OR (NOT)’s independently and then com-
bine 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 IR 00000 is a LOAD instruction and the condition below it is an OR
instruction between the status of IR 00000 and that of IR 00001. The condition at
IR 00002 is another LOAD instruction and the condition below is an OR NOT
instruction, i.e., an OR between the status of IR 00002 and the inverse of the
status of IR 00003. 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 lad-
der diagram is shown below. 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 in-
put.
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 IR 00000 is ON and IR 00001 is OFF or
when IR 00002 and IR 00003 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 un-
used execution condition.
Instruction
00000 00001
00002 00003
Address Instruction Operands
00000 LD 00000
00001 AND NOT 00001
00002 LD 00002
00003 AND 00003
00004 OR LD ---
Naturally, some diagrams will require both AND LOAD and OR LOAD instruc-
tions.
OR LOAD