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(c) Specifying the latch range of internal user devices
Device data of the Universal model QCPU can be latched by specifying a latch range of internal user devices in
the same way as for the Basic model QCPU and High Performance model QCPU.
The ranges can be set in the Device tab of the PLC parameter dialog box.
Internal user devices that can be latched are as follows:
• Latch relay (L)
• Link relay (B)
• Annunciator (F)
• Edge relay (V)
•Timer (T)
• Retentive timer (ST)
• Counter (C)
• Data register (D)
• Link register (W)
● If latch ranges of internal user devices are specified in the Universal model QCPU, the processing time will be added to
the scan time in proportion to the device points set to be latched. (For example, if 8K points are latched for the latch
relay (L), the scan time will be 28.6
s.) To shorten the scan time, remove unnecessary latch device points to minimize
the latch range.
● The scan time will not increase when a latch range of the file register (R, ZR) is specified.
(4) How to shorten the scan time
When data to be latched are stored in the file register (R, ZR), the processing time is shorter than that
for latching internal user device.
*1: Time indicates the time required additionally when the file register is stored in the standard RAM.
Example Reducing the latch points of the data register (D) from 8K points to 2K points,
and using the file register (ZR) instead (when the Q06UDHCPU is used)
TableApp.40 Differences between before and after moving latch points of the data register (D) to the file register (ZR)
Item Before After
Latch points of the data register (D) 8192 (8K) points
2048 (2K) points
(6K points are moved to the file
register.)
Number of devices in the program
Data register (D) (Latch range) 400 100
File register (ZR) (Standard RAM) 0 300
Additional scan time 0.41ms
0.13ms
*1
Number of steps increased --- 300 steps