3.1 Basic Functionality
3.1.4 Scans
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3
CPU Module Functionality
Keep Latest Value Setting in High-speed/Low-speed Scans
You can use the Keep Latest Value setting to specify the number of scans to hold previous data
when an input error occurs. If the input error still exists after the number of scans specified for
the Keep Latest Value setting, the input values will be treated as 0. When the input error is
removed, reading the input values is resumed automatically. There are separate Keep Latest
Value settings for the high-speed scan and the low-speed scan.
Operation
The following figure illustrates the operation for the Keep Latest Value setting.
Keep Latest Value setting: 3 scans for high-speed scan
Setting Procedure
Perform the following procedure with MPE720 version 7 to set the Keep Latest Value setting.
1.
Select File
−
Environment Setting from the menu bar. Alternatively, click the System
Setting Icon on the Start Tab Page.
The Environment Setting Dialog Box will be displayed.
2.
Select Setup
−
System Setting.
The following dialog box will be displayed.
Observe the following precautions when setting the high-speed scan time and low-speed
scan time.
1. Set the scan set value so that it is 1.25 times greater than the maximum value.
If the scan set value is too close to the maximum value, the refresh rate of the MPE720 window
will noticeably drop and can cause communications timeout errors to occur. If the maximum
value exceeds the scan set value, a watchdog error may occur and cause the Machine Con-
troller system to shut down.
2. If you are using MECHATROLINK-II or MECHATROLINK-III, set values that are an integral mul-
tiple of the communications cycle. If you change the communications cycle, check the scan
time set values.
3. Do not change the scan set value while the Servo is ON. Never change the scan set value
while an axis is in motion (i.e., while the motor is rotating). Doing so may cause the motor to
rotate out of control.
4. After changing or setting a scan time, always save the data to flash memory.
High-speed
scan
Keep Latest Value region:
The value from before
the input error (201) is held for 3 scans.
100 101 102 103 104 105
200 201
201
0
106 107
207
Input value to
I/O Module 1
Input value
to I/O
Module 2
The number of scans set
for the Keep Latest
Value setting was
exceeded, so the input
value is treated as 0.
Reading the input
value is automatically
started again.
Input error occurred in
I/O Module 2.
Input error removed
from I/O Module 2.
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