7
PROGRAMMING CAUTIONS
7.4 Precautions at System Switching Occurrence
7
- 21
1
OV
ER
VIE
W
2
SYS
TEM
CONFIGURA
TI
ON
3
TR
AC
KI
N
G
C
ABL
E
4
P
R
OCE
DURE
FO
R
S
TAR
TING
UP
A
RE
DUN
DAN
T
S
Y
S
T
E
M
5
RE
DUNDA
NT S
Y
S
T
E
M
FUNCTIONS
6
RE
DUN
DAN
T
S
Y
S
T
E
M
NE
TW
O
R
K
S
7
PR
OG
R
A
MM
IN
G
CA
UTIO
N
S
8
TR
O
U
BLE
S
HOOTING
3) When output (output (Y), writing to buffer memory) is performed from the timer
contact, the timer goes into the above-mentioned 2) status, which leads to
chattering of the output.
When the CPU module communicates with the module or external device
using the output (Y) and buffer memory, the program may not operate normally
due to chattering of the output after system switching.
The operation for the case where the system switching occurs before the
tracking transfer processing is completed after outputting the output (Y) from
the timer contact is shown in Diagram 7.19.
[Program example]
Diagram 7.19 Chattering Occurs to Output by Timer Contact
M0
T0
K10
T0
SET
Y10
0
END
END
END
0
0
END
0
0
0
Control system CPU module
Program
OUT TO
OUT TO
OUT TO
M0
ON
ON
ON
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
Coil of T0
Contact of T0
Y10 of CPU module
External output of Y10
Standby system CPU module
New control system CPU module
Tracking transfer processing
Tracking transfer processing
Scan execution type program
Scan execution type
program
Scan execution type
program
Scan execution type
program
Reflect tracking
data transfer
Reflect tracking
data transfer
Prepare tracking
transfer data
Prepare tracking
transfer data
Error
occurrence
Send
Wait
Wait
Receive
Send
Receive
Send
Receive
Output
Output
Output
Output
System switching
ON
ON
ON
ON
END processing
END processing
END processing
OUT TO
END processing
