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6.1.1 Communications by auto refresh (using the auto refresh area)
This section describes data communications by auto refresh using the auto refresh area in the CPU shared memory.
Data communications by auto refresh can also be performed using the auto refresh area in the multiple CPU high speed
transmission area. Use of the multiple CPU high speed transmission area can reduce the increase in scan time. Some
conditions apply to using the area. ( Page 135, Section 6.1.2)
(1) Communications by auto refresh
(a) Overview
Auto refresh communicates data using the auto refresh area in the CPU shared memory. Data are
automatically read/written among all the CPU modules in the multiple CPU system by setting "Communication
Area Setting (Refresh 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)
• Processing performed during END processing of CPU No.1
1) CPU No.1 transfers the device data (B0 to B1F) to the auto refresh area in its own CPU shared memory.
4) CPU No.1 reads the data in the auto refresh area of the CPU No.2’s CPU shared memory and stores
them in B20 to B3F of its own.
• Processing performed during END processing of CPU No.2
2) CPU No.2 transfers the device data (B20 to B3F) to the auto refresh area in its own CPU shared
memory.
3) CPU No.2 reads the data in the auto refresh area of the CPU No.1’s CPU shared memory and stores
them in B0 to B1F of its own.
CPU No.1
CPU shared memory
Device
CPU No.2
CPU shared memory
3)
1)
2)
Device
4)
Host CPU operation information area
System area
Auto refresh area
User setting area
Data are written during END
processing of CPU No.1.
B0 to B1F (for CPU No.1)
B20 to B3F (for CPU No.2)
Data are read during
END processing of
CPU No.2.
Data are read during
END processing of
CPU No.1.
Host CPU operation information area
System area
Auto refresh area
User setting area
Data are written during
END processing of
CPU No.2.
B0 to B1F (for CPU No.1)
B20 to B3F (for CPU No.2)