7
- 10
7.2 Cautions on Fixed-Scan Clocks and Fixed Scan Execution Type Programs
7
PROGRAMMING CAUTIONS
(3) Fixed scan execution type Program
When system switching occurs, the execution of fixed scan execution type programs
is suspended until system switching is complete.
When system switching is complete, the new control system CPU module starts
counting the fixed-scan interval time from 0.
Therefore, the fixed scan execution interval time is increased (T+ ') as shown in
Diagram 7.8.
The maximum value for the extension time is (T+ ) when = '.
Diagram 7.8 Operations of Fixed Scan Execution Type Programs at System Switching
Begin system switching
System Switching complete
T : System switching time
System switching activated
Control system
Control system
New standby system
New standby system
New control system
Standby system
Standby system
New control system
Scan execution type
Program
fixed cycle execution type
Program
Scan execution type
Program
fixed cycle execution type
Program
T
Extension of fixed
cycle interval
: Fixed Cycle Interval
: Period between starting scan execution
type program and system switching