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APPENDICES
A
Appendix 5 Replacing Basic Model QCPU or Qn(H)CPU with QnUCPU
Appendix 5.4 Functions
(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.
*1
(For example, if 8K points are latched for the latch relay (L),
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
(ZR) instead (when the Q06UDHCPU is used)
*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 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
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