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CHAPTER 5 DEVICES
5
5.5 Index Register/Standard Device Register (Z)
5.5.3 Saving and restoration of the index register
5.5.3 Saving and restoration of the index register
The CPU module performs the following when switching from the scan execution type program to the interrupt/fixed
scan execution type program.
• Saving and restoring the index register data
• Saving and restoring block numbers of the file register
(1) Setting for saving and restoration
Configure the setting for saving and restoration using a programming tool.
Project window [Parameter] [PLC Parameter] [PLC System]
When not writing data to the index register during interrupt/fixed scan execution type program, select "High Speed
Execution" in the Interrupt Program/Fixed Scan Program Setting area. This setting enables faster program
switching because saving and restoration are not performed.
(2) Processing of the index register
(a) When "High speed execution" is not selected
*1 The Z0 value is changed to 3 in the interrupt program.
To pass index register values from the interrupt/fixed scan execution type program to the scan execution type program, use
word devices.
Selecting this
saves or restores
index register data.
Execution program
Z0 = 1 Z0 = 1 Z0 = 3
Z0 = 0
Z0 = 1
Passed
Switching
Saved
Restored
Restored
Z0 = 1 Z0 = 1 Z0 = 1
Z0 = 1
Index register save area
Index register value
Scan execution
type program
Scan execution
type program
Interrupt/fixed
scan execution
type program
for scan execution
type program
1) The CPU module saves the index register
values and passes them at program
switching.
2) The CPU module restores the index
register values saved at program switching.
*
1
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