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4.A2CCPU
- - - - - - - - - - - - - - - - - - - - MELSEC-A
4.2.5
Status latch
The monitoring function of a peripheral cannot confirm the status of each
I
device all the time. The status latch function transfers and saves the device
data to the status latch area when the SlT instruction is executed in the
sequence program.
The device data saved using the SlT instruction can be read by the
GPP/PHP/HGP to monitor it.
Status
latch
area
File
register
area
Device
memory
area
A2CCPU
GPP/PHP/HGP
~-------------------------------,
r-----------------------------,
Transfer
I ,
I
by SlT
:
Reading:
0" I f :
Instruction
:in the PC:
ISP't
ay
. or
:
mode :
mom
onng
:
+i,:
~~~~~s
. . .
<J~,:
area
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
,
L
~
Fig. 4.17 Status Latch Sequence
(1) Application
The status latch function can be used to check the device data when a
t
fault condition exists during debugging.
,
It is also used to find causes when a fault condition exists during
sequence program execution by making a program that will execute the
SlT instruction if such a condition exists.
(2)
Processing
(a) The following data is stored in the status latch area when the SlT
instruction is executed.
41
1) Device memory
X, Y, M, l, S, F, B
ON/OFF data
T, C
Contact and coil ON/OFF data and present
value
D, W, A, Z, V
: Stored data
2) File register (R)
Stored data
4-28

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