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Appendix 4.2 Factors that increase scan time
The processing time in a multiple CPU system increases from that in a single CPU system when the following
functions are used.
When any of the following functions is used, add the time values described in this section to the values calculated on
Page 192, Appendix 4.1.
• Auto refresh of the CPU shared memory (including the multiple CPU high speed transmission function)
• Refresh of CC-Link IE and MELSECNET/H
• Auto refresh of CC-Link
(1) Auto refresh of the CPU shared memory (including the multiple CPU high
speed transmission function)
(a) Auto refresh time of the CPU shared memory
This is the time required for executing refresh set in "Communication Area Setting (Refresh Setting)" and
"Multiple CPU High Speed Transmission Area Setting" of PLC parameter ("Multiple CPU Setting"). The value is
the total amount of time required for the CPU module to write data to its own CPU shared memory and read
data from the CPU shared memory of other CPU modules.
The time value needs to be added when refresh is set in "Communication Area Setting (Refresh Setting)" and
"Multiple CPU High Speed Transmission Area Setting" of PLC parameter ("Multiple CPU Setting").
(b) Calculating formula
The time value is obtained by the following calculation.
• For the Basic model QCPU
The number of receive word points is the sum of the number of word points sent by other CPU modules.
Ex.
When the number of CPU modules is 3 and the host CPU is CPU No.1
The number of receive word points will be the sum of the number of word points sent by CPU No.2 and
No.3.
Use the following values for N1 to N5.
Basic model QCPU N1 N2 N3 N4 N5
Q00CPU 63µs 1.13µs 63µs 161µs 0.88µs
Q01CPU 57µs 1.03µs 57µs 146µs 0.80µs
(N1 + (Number of send word points) N2) +
(N3 + (Number of other CPU modules) N4 + (Number of receive word points) N5) (µs)
(Auto refresh time)
=