2. INSTRUCTIONS
2 − 3
MELSEC-A
3)….. Indicates the instruction symbol used for the program. The instruction symbol
is shown on a 16-bit instruction basis. The symbols of a 32-bit instruction and
an instruction executed only at the rise from OFF to ON are as indicated
below:
Instruction executed only at the rise from OFF to ON………P
is added to the end of instruction.
4)….. Indicates the symbol diagram in the circuit.
Destination: Indicates the destination of data after operation.
Source: Stores data before operation.
5)….. Indicates the processing of each instruction.
32-bit instruction………D is added to the head of instruction.
+D
+
Example:
16-bit instruction 32-bit instruction
Example:
+
P
+
Instruction executed
during ON
Instruction executed only
at the rise from OFF to ON
Indicates destination.
Indicates source.
Indicates instruction
symbol.
Indicates destination.
Indicates source.
Indicates instruction
symbol.
Fig. 2.1 Symbol Representations in Ladder
(D) + (S) → (D)
Indicates 16 bits.
(D + 1, D) + (S + 1, S) → (D + 1, D)
16 bits, 16 bits
Indicates 32 bits.
Upper 16 bits Lower 16 bits
D + 1 D
Fig. 2.2 Processing of Each Instruction
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