43
If there is no End instruction anywhere in the program, the program will not
be executed at all.
4–6 Programming Precautions
The number of conditions that can be used in series or parallel is unlimited.
Therefore, use as many conditions as required to draw a clear diagram. Al-
though very complicated diagrams can be drawn with instruction lines almost
forming mazes, there must not be any conditions on instruction lines running
vertically between two other instruction lines. Diagram A shown below, for
example, is not possible, and should be redrawn as diagram B.
Instruction 2
Instruction 1
0002
0003
0000
0001
0004
Diagram A
Instruction 1
0004
0003
0000
0001
Diagram B
0002
Instruction 2
00040000
0001
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.
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 , be-
low, must be redrawn as diagram B. If an instruction must always be exe-
cuted (e.g., if an output must always be kept ON while the program is being
executed), the Always ON Flag (1813) in the SR area can be used.
Instruction
1813
Instruction
Diagram A
Diagram B
There are, however, 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 condi-
Programming Precautions Section 4–6
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