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1 MULTIPLE CPU SYSTEM
1.3 Data Communication Between CPU Modules in the Multiple CPU System
Fixed scan data transmission section over check
A check is performed to verify whether Motion CPU fixed-cycle processing (Motion SFC event tasks, motion operations, etc.)
is completed by the data transmission section of the CPU fixed scan communication.
A check can be carried out to detect whether fixed scan transmission data separation has occurred. "Detect/Not detected"
and "Stop/Continue" can be selected in the "RAS settings" (Page 55 CPU parameter).
Checks are performed as follows depending on the relationship between the motion operation cycle and fixed scan
communication cycle.
When motion operation cycle < fixed scan communication cycle
A check is performed only when an operation cycle over condition is detected, and not performed otherwise.
When motion operation cycle = fixed scan communication cycle
A check is performed every cycle.
When motion operation cycle > fixed scan communication cycle
A check is performed only at the fixed scan communication section immediately before the motion operation cycle. No check
is performed part of the way into a fixed scan communication section during a motion operation cycle, thus if a cycle shorter
than the motion operation cycle is referenced from another CPU, separation may occur even if no error occurs when
performing this check.
Special relay/special register
The special relay and special register relating to the fixed scan data communication section excess check are shown below.
Refer to the following for details on special relays and special registers.
• Special relay(Page 426 Special Relays)
• Special register(Page 431 Special Registers)
Device Number Name
Special relay SM484 Fixed scan data transmission section over
Special register SD484 Fixed scan data transmission section over count
Fixed scan
transmission
section
OK (the send data can be seen
from other CPU in next cycle)
Fixed scan
transmission
section
Motion operation time
Fixed scan communication cycle
NG (the send data cannot be seen from
other CPU in the next cycle because data
write was not completed by the beginning
of the transmission section)
Receipt
refresh
Receipt
refresh
Motion CPU
fixed-cycle
processing
Transmission
refresh
Transmission
refresh
Operation
cycle
Motion operation time
Operation cycle
Fixed scan communication cycle
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