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(2) Communications by auto refresh
(a) Overview
Auto refresh communicates data using the auto refresh area of the multiple CPU high speed transmission area
in the CPU shared memory. The data written to the auto refresh area of the multiple CPU high speed
transmission area is sent to that of the other CPU modules at regular intervals (multiple CPU high speed
transmission cycles).
Data are automatically read/written among all the CPU modules in the multiple CPU system by setting "Multiple
CPU High Speed Transmission Area Setting" in PLC parameter ("Multiple CPU Setting").
Since auto refresh automatically reads device data in other CPU modules, the host CPU module can use those
device data.
Auto refresh increases the scan time in the multiple CPU system. ( Page 192, Appendix 4)
Ex.
Operations when CPU No.1 performs auto refresh of data in B0 to B1F (32 points) and CPU No.2
performs auto refresh of data in B20 to B3F (32 points)
• Procedure for CPU No.2 to read device data of CPU No.1
1) CPU No.1 transfers device data (B0 to B1F) to the auto refresh area in its own CPU shared memory
during END processing.
2) CPU No.1 sends the data in the multiple CPU high speed transmission area of its own to CPU No.2.
3) CPU No.2 transfers the received data to B0 to B1F of its own during END processing.
• Procedure for CPU No.1 to read device data of CPU No.2
4) CPU No.2 transfers device data (B20 to B3F) to the auto refresh area in its own CPU shared memory
during END processing.
5)CPU No.2 sends the data in the multiple CPU high speed transmission area of its own to CPU No.1.
6) CPU No.1 transfers the received data to B20 to B3F of its own during END processing.
CPU No.1
CPU shared memory
CPU No.2
CPU shared memory
1)
6)
3)
4)
2)
5)
Device Device
Multiple CPU high speed transmission
area of CPU No.1
Auto refresh area
Multiple CPU high speed transmission
area of CPU No.2
Auto refresh area
Data are written during END
processing.
Data are read during END
processing.
B0 to B1F (for CPU No.1)
B20 to B3F (for CPU No.2)
Data are sent to
CPU No.2.
Data are sent to
CPU No.1.
Multiple CPU high speed transmission
area of CPU No.1
Auto refresh area
Multiple CPU high speed transmission
area of CPU No.2
Auto refresh area
Data are written during END
processing.
Data are read during END
processing.
B0 to B1F (for CPU No.1)
B20 to B3F (for CPU No.2)