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Although simple in appearance, the diagram below requires an AND LOAD
instruction.
Instruction
0002
0003
0000
0001
Address
Instruction
Operands
0000
LD
0000
0001
OR
0001
0002
LD
0002
0003
OR NOT
0003
0004
AND LD
---
The two logic blocks are indicated by dotted lines. Studying this example
shows that an ON execution condition would be produced when both 1)
either of the conditions in the left logic block was ON (i.e., when either 0000
or 0001 was ON) and 2) either of the conditions in the right logic block was
ON (i.e., when either 0002 was ON or 0003 was OFF).
Analyzing the diagram in terms of instructions, the condition at 0000 would
be a LOAD instruction and the condition below it would be an OR instruction
between the status of 0000 and that of 0001. The condition at 0002 would be
another LOAD instruction and the condition below this would be an OR NOT
instruction, i.e., an OR between the status or 0002 and the inverse of the
status of 0003. 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 allows us to do this. AND LOAD
always takes an AND between the current execution condition and the last
unused execution condition. An unused execution condition is produced by
using the LOAD or LOAD NOT instruction for any but the first condition on an
instruction line.
Although we’ll not describe it in detail, the following diagram would require 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 0000 was ON and 0001 was OFF or when 0002 and 0003 were
both ON.
Instruction
0000
0001
0002
0003
Address
Instruction
Operands
0000
LD
0000
0001
AND NOT
0001
0002
LD
0002
0003
AND
0003
0004
OR LD
---
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 combined, working progressively back to the
first block. Although either of these methods will produce exactly the same
result, the second method, that of coding all logic block instructions together,
can be used only if eight or fewer blocks are being combined, i.e., if seven or
fewer logic block instructions are required.
AND LOAD
OR LOAD
Logic Block Instructions in
Series
The Ladder Diagram
Section 4-3
Summary of Contents for SYSMAC C20K
Page 1: ...Cat No W146 E1 5 Programmable Controllers SYSMAC C20K C28K C40K C60K ...
Page 2: ...K type Programmable Controllers OPERATION MANUAL Revised July 1999 ...
Page 3: ...iv ...
Page 5: ...vi ...
Page 19: ...7 SECTION 2 Hardware Considerations 2 1 Introduction 2 2 Indicators 2 3 PC Configuration ...