7
PROGRAMMING CAUTIONS
7.2 Cautions on Fixed-Scan Clocks and Fixed Scan Execution Type Programs
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(6) Interrupt during Tracking Processing
If interrupt is enabled (EI status) during END processing, when an interrupt is issued
during tracking processing, the CPU will stop the tracking processing and execute the
interrupt program.
Therefore, both data of before and after interrupt program execution might be tracked.
[Example]
The operations for interrupted (I31) execution via an internal timer are shown in
Diagram 7.10.
When execution of programs interrupted during tracking processing is not done,
execute DI instructions, then execute EI instructions at step 0 before executing END
instructions, as shown in the program in the Diagram 7.11.
As interrupt is disabled during END processing (including tracking processing), the
CPU will not execute the interrupt program.
Diagram 7.10 Operations When Interrupt Is Executed by Internal Timer
Diagram 7.11 Program Example That Disables Interrupts during END Processing
10ms
Execute interrupt
program (I31)
Execute Tracking
transfer process
Tracking transfer of data before
executing interrupt program
Cancel tracking transfer process
(execute interrupt program)
Tracking transfer of data after
executing interrupt program
EI
0
END
DI
Allow interrupt.
Prevent interrupt.
