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MELSEC-Q
10 DEVICES
10.6.2 Switching between scan/low speed execution type programs and interrupt/fixed scan
execution type programs
The "PLC system" tab screen in the “(PLC) Parameter" dialog box provides the option
to save (protect) or restore index register data (Z0 to Z15) when switching between a
scan execution type program and a low speed execution type program or between an
interrupt program and a fixed scan execution type program.
When not writing date to index registers check by using an interrupt program/fixed
scan execution type program, the "High speed execution" check box in the "Interrupt
program/Fixed scan program setting" section at the "PLC system" tab screen in the
“(PLC) Parameter" dialog box. This will switch between programs quickly.
(1) When the "High speed execution" check box is OFF:
(a) When the scan/low speed execution type program is switched to the
interrupt/fixed scan execution type program, the scan/low speed execution
type program's index register value is first saved, and is then transferred to
the interrupt/fixed scan execution type program.
(b) When the interrupt/fixed scan execution type program is switched to the
scan/low speed execution type program, the saved index register value is
reset.
Executed program
Index register value
Scan/low speed
execution type
program
Switch-
ing
Z0=1
Z0=0
Z0=1
Index register storage area
For scan/low speed
execution type program
Interrupt program/
Fixed scan execution
type program
Z0=1 to Z0=3
Z0=1
Reset
Z0=1
Z0=1
Z0=1
Scan/low speed
execution type
program
Saved
Reset
Transf-
erred
: For interrupt program, Z0 is changed to 3.
Word devices should be used to transfer index register data from an
interrupt or fixed scan execution type program to a scan or low speed
execution type program.