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LOAD and LOAD NOT The first condition that starts any logic block within a ladder diagram corre-
sponds to a LOAD or LOAD NOT instruction. Each of these instruction requires
one line of mnemonic code. “Instruction” is used as a dummy instruction in the
following examples and could be any of the right-hand instructions described lat-
er in this manual.
00000
00000
A LOAD instruction.
A LOAD NOT instruction.
Address Instruction Operands
00000 LD 00000
00001 Instruction
00002 LD NOT 00000
00003 Instruction
When this is the only condition on the instruction line, the execution condition for
the instruction at the right is ON when the condition is ON. For the LOAD instruc-
tion (i.e., a normally open condition), the execution condition will be ON when IR
00000 is ON; for the LOAD NOT instruction (i.e., a normally closed condition), it
will be ON when 00000 is OFF.
AND and AND NOT When two or more conditions lie in series on the same instruction line, the first
one corresponds to a LOAD or LOAD NOT instruction; and the rest of the condi-
tions correspond to AND or AND NOT instructions. The following example
shows three conditions which correspond in order from the left to a LOAD, an
AND NOT, and an AND instruction. Again, each of these instructions requires
one line of mnemonic code.
00000 00100 LR 0000
Instruction
Address Instruction Operands
00000 LD 00000
00001 AND NOT 00100
00002 AND LR 0000
00003 Instruction
The instruction will have an ON execution condition only when all three condi-
tions are ON, i.e., when IR 00000 is ON, IR 00100 is OFF, and LR 0000 is ON.
AND instructions in series can be considered individually, with each taking the
logical AND of the execution condition (i.e., the total of all conditions up to that
point) and the status of the AND instruction’s operand bit. If both of these are ON,
an ON execution condition will be produced for the next instruction. If either is
OFF, the result will also be OFF. The execution condition for the first AND
instruction in a series is the first condition on the instruction line.
Each AND NOT instruction in series takes the logical AND of its execution condi-
tion and the inverse of its operand bit.
Basic Ladder Diagrams Section 4-4