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Except for instructions for which conditions are not allowed (e.g., INTERLOCK
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 instruc-
tion 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.
Instruction
25313
Instruction
Diagram A: Incorrect
Diagram B
Address Instruction Operands
00000 LD 25313
00001 Instruction
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 5-8-2 AND LOAD and OR LOAD for
more details and Section 7 Program Monitoring and Execution for further exam-
ples.
00000
00001 00207
00207
00001
00000
00207
00207
Diagram A
Diagram B
Address Instruction Operands
00000 LD 00000
00001 LD 00001
00002 AND 00207
00003 OR LD ---
00004 OUT 00207
Address Instruction Operands
00000 LD 00001
00001 AND 00207
00002 OR 00000
00003 OUT 00207
Programming Precautions Section 4-10