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CHAPTER 6 COMMUNICATIONS AMONG CPU MODULES
6
6.1 Communications Using the CPU Shared Memory
6.1.3 Communications by programs using the CPU shared memory
(8) Precautions
(a) Start I/O numbers of CPU modules
Set the following start I/O numbers to each CPU module for the read/write instructions.
(b) Writing data to the CPU shared memory
Do not write data to the following areas in the CPU shared memory. ( Page 118, Section 6.1)
• System area
• Auto refresh area
• Use-prohibited area
(c) Reading data from the CPU shared memory
Do not read data from the following areas in the CPU shared memory when a High Performance model QCPU
or Process CPU is used.( Page 118, Section 6.1)
• System area
• Auto refresh area
(d) Accessing a module in RESET status
No error will occur even if the CPU module accessed by a read instruction is in RESET status.
However, the access execution flag (SM390) will remain off even after the instruction execution has been
completed. (This will not apply to Universal model QCPUs.)
(e) Accessing CPU modules simultaneously
Configure an interlock to prevent simultaneous access during data communications by the read/write
instructions. If accessed, old data and new data may coexist (data inconsistency). ( Page 154, Section
6.1.3 (7))
(f) Writing data to the CPU shared memory of other CPU modules
Data cannot be written to the CPU shared memory of other CPU modules by a write instruction.
If data are written by executing the TO, S.TO instructions or those using the cyclic transmission area device
(U3En\G), "SP. UNIT ERROR" (error code: 2115) will occur.
CPU No. CPU No.1 CPU No.2 CPU No.3 CPU No.4
Start I/O number
3E0
H
3E1
H
3E2
H
3E3
H