Omron C200H Operation Manual page 106

Programming Precautions
Diagram A: Incorrect
25313
00000
00001 00207
00001 00207
00000
The number of times any particular bit can be assigned to conditions is not
limited, so use them as many times as required to simplify your program.
Often, complicated programs are the result of attempts to reduce the number
of times a bit is used.
Except for instructions for which conditions are not allowed (e.g., INTER-
LOCK CLEAR and JUMP END, see below), every instruction line must also
have at least one condition on it to determine the execution condition for the
instruction at the right. Again, diagram A , below, must be drawn as diagram
B. If an instruction must be continuously executed (e.g., if an output must
always be kept ON while the program is being executed), the Always ON
Flag (SR 25313) in the SR area can be used.
Diagram B
There are a few exceptions to this rule, including the INTERLOCK CLEAR,
JUMP END, and step instructions. Each of these instructions is used as the
second of a pair of instructions and is controlled by the execution condition of
the first of the pair. Conditions should not be placed on the instruction lines
leading to these instructions. Refer to Section 5 Instruction Set for details.
When drawing ladder diagrams, it is important to keep in mind the number of
instructions that will be required to input it. In diagram A, below, an OR LOAD
instruction will be required to combine the top and bottom instruction lines.
This can be avoided by redrawing as shown in diagram B so that no AND
LOAD or OR LOAD instructions are required. Refer to 5-6-2 AND LOAD and
OR LOAD for more details and Section 7 Program Monitoring and Execution
for further examples.
Diagram A
Diagram B
Instruction
Address Instruction
Instruction
00000 LD
00001 Instruction
Address Instruction
00207
00000
00001
00002
00003
00004
Address Instruction
00000
00207
00001
00002
00003
Section 4-9
Operands
25313
Operands
LD 00000
LD 00001
AND 00207
OR LD
OUT 00207
Operands
LD 00001
AND 00207
OR 00000
OUT 002
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