46
tion in the following examples and could be any of the right-hand instructions
described later 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
instruction (i.e., a normally open condition), the execution condition would be
ON when IR 00000 was ON; for the LOAD NOT instruction (i.e., a normally
closed condition), it would be ON when 00000 was OFF.
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 conditions, 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 would have an ON execution condition only when all three
conditions are ON, i.e., when IR 00000 was ON, IR 00100 was OFF, and LR
0000 was 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 a series would take the logical AND between
its execution condition and the inverse of its operand bit.
When two or more conditions lie on separate instruction lines running in par-
allel and then joining together, the first condition corresponds to a LOAD or
LOAD NOT instruction; the rest of the conditions correspond to OR or OR
NOT instructions. The following example shows three conditions which corre-
AND and AND NOT
OR and OR NOT
Basic Ladder Diagrams
Section 4-3