Mitsubishi MELSEC User Manual page 29

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OVERVIEW
(4) Enhanced RAS
(a) Enhanced memory diagnostics
(b) Redundant CPU
(c) Enhanced hardware diagnostics by hardware circuit
Overvoltage/
undervoltage detection
Clock stop detection
The memory diagnostics equipped with the CPU module are enhanced.
The CPU module has two CPUs (CPU A and CPU B). The operation results of
CPU A/CPU B are compared, and output only when the results are matched so
that incorrect outputs can be prevented. (When the compared results are
mismatched, the system stops.)
The diagnostic functions of the Table1.3 prevents incorrect outputs when a
hardware error which cannot be detected by the OS occurs.
Table1.3 Hardware diagnostics function added to the QS series CPU module
Diagnostics
Overvoltage or undervoltage is detected for the power supply voltage
provided from the power supply module to the CPU module.
The input clock stop to the CPU module internal circuit is detected.
CPU module
CPU CPU
A B
Operation Operation
Compare
result result
Output when matched
Figure 1.2 Redundant CPU
Diagnosis Contents
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1.1 Features
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