Mitsubishi Electric MELSEC-Q00U(J)CPU User Manual page 553

(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)
The following devices also can be set when a file register is set to be used in the PLC file.
• File register (R, ZR)
• Extended data register (D)
• Extended 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.
the scan time will be 28.6µs.) To shorten the scan time, remove unnecessary latch device points to minimize the latch range.
*1 For file registers (including an extended data register (D) and an extended link register (W)), the scan time is not
increased due to latch.
(4) How to shorten the scan time
When data to be latched are stored in the file register the processing time is shorter than that for latching internal
user device.
Reducing the latch points of the data register (D) from 8K points to 2K points, and using the file register
Ex.
(ZR) instead (when the Q06UDHCPU is used)
Latch points of the data register (D)
Number of devices in the program
Additional scan time
Number of steps increased
*1 Time indicates the time required additionally when the file register is stored in the standard RAM.
The High-speed Universal model QCPU and Universal model Process CPU can choose a latch interval setting between
"Each Scan" and "Time Setting" in parameter. When "Time Setting" is selected, latch data processing starts during the first
END processing after a preset time has elapsed. Since the latch data processing is performed asynchronous to the
sequence program, an increase in scan time is reduced.
Item
Data register (D) (Latch range)
File register (ZR) (Standard RAM)
*1
(For example, if 8K points are latched for the latch relay (L),
Before
8192 (8K) points (6K points are moved to the file
400
0
0.41ms
---
APPENDICES
After
2048 (2K) points
register.)
100
300
*1
0.13ms
300 steps
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