Differentiated Instructions - Omron CPM1 Programming Manual

7-4

Differentiated Instructions

00000
00000
Most instructions are provided in both differentiated and non-differentiated
forms. Differentiated instructions are distinguished by an @ in front of the
instruction mnemonic.
A non-differentiated instruction is executed each time it is scanned as long as its
execution condition is ON. A differentiated instruction is executed only once af-
ter its execution condition goes from OFF to ON. If the execution condition has
not changed or has changed from ON to OFF since the last time the instruction
was scanned, the instruction will not be executed. The following two examples
show how this works with MOV(21) and @MOV(21), which are used to move the
data in the address designated by the first operand to the address designated by
the second operand.
Diagram A
Diagram B
In diagram A, the non-differentiated MOV(21) will move the content of HR 10 to
DM 0000 whenever it is scanned with 00000. If the cycle time is 80 ms and 00000
remains ON for 2.0 seconds, this move operation will be performed 25 times and
only the last value moved to DM 0000 will be preserved there.
In diagram B, the differentiated @MOV(21) will move the content of HR 10 to DM
0000 only once after 00000 goes ON. Even if 00000 remains ON for 2.0 seconds
with the same 80 ms cycle time, the move operation will be executed only once
during the first cycle in which 00000 has changed from OFF to ON. Because the
content of HR 10 could very well change during the 2 seconds while 00000 is
ON, the final content of DM 0000 after the 2 seconds could be different depend-
ing on whether MOV(21) or @MOV(21) was used.
All operands, ladder diagram symbols, and other specifications for instructions
are the same regardless of whether the differentiated or non-differentiated form
of an instruction is used. When inputting, the same function codes are also used,
but NOT is input after the function code to designate the differentiated form of an
instruction. Most, but not all, instructions have differentiated forms.
Refer to 7-11 INTERLOCK and INTERLOCK CLEAR -- IL(02) and IL(03) for the
effects of interlocks on differentiated instructions.
The CPM2A/CPM2C also provides differentiation instructions: DIFU(13) and
DIFD(14). DIFU(13) operates the same as a differentiated instruction, but is
used to turn ON a bit for one cycle. DIFD(14) also turns ON a bit for one cycle, but
does it when the execution condition has changed from ON to OFF. Refer to
7-8-4 DIFFERENTIATE UP and DOWN - DIFU(13) and DIFD(14) for details.
Address Instruction
MOV(21)
00000 LD
HR 10
00001 MOV(21)
DM 0000
Address Instruction
@MOV(21)
00000 LD
HR 10
00001 @MOV(21)
DM 0000
Section 7-4
Operands
00000
HR 10
DM 0000
Operands
00000
HR 10
DM 0000