Reducing Processing Time - Mitsubishi Electric MELSEC Q Series User Manual

5.3 Reducing processing time

(1) Multiple CPU system processing
Access is made between a CPU module and an I/O module or intelligent function module through a bus (base
unit pattern, extension cable) and this bus cannot be used by multiple CPU modules at the same time.
If more than one CPU module attempt to use it simultaneously, the CPU module attempted access later is placed
in "Standby" status until the processing of the first CPU module is completed.
In the multiple CPU system, this waiting time (time of "Standby status") will cause delay in input and output and
increase in scan time.
(2) Maximum standby time
In the multiple CPU system, waiting time of the host CPU will reach the maximum when:
• Using the maximum number of CPU modules
• Using extension base unit(s)
• An intelligent function module on an extension base unit has high volume of data
• Simultaneous accesses are made to a module on the extension base unit where the maximum number of
CPU modules is mounted.
(3) Reducing processing time for multiple CPU system
The following methods are available for reducing the processing time in the multiple CPU system.
• Place modules of high access points (e.g. CC-Link IE controller network, MELSECNET/H, or CC-Link)
together on the main base unit.
• Set one QCPU as the control CPU to control the modules of high access points (e.g. CC-Link IE controller
network, MELSECNET/H, or CC-Link) to prevent simultaneous access.
• Reduce the number of refresh points of the CC-Link IE controller network, MELSECNET/H, and CC-Link etc.
• Reduce the number of auto refresh points between CPU modules.
It is possible to reduce scan time by changing the following PLC parameter settings:
• A Series CPU compatibility setting
• Floating point arithmetic processing
User's Manual (Function Explanation, Program Fundamentals) for the CPU module used.
íç1
Basic
Note5.6
TFor the Basic model QCPU and the Universal model QCPU, A series CPU compatibility setting cannot be made.
Note5.7
Universal
For the Basic model QCPU, the Process CPU or Universal model QCPU, the floating point calculation processing
cannot be changed.
Universal
Basic Process
CHAPTER5 PROCESSING TIME OF QCPU IN MULTIPLE CPU SYSTEM
Note5.6
Note5.7íç1
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