Allen-Bradley GuardPLC 1753, Safety Reference Manual

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Publication 1753-RM002C-EN-P - September 2008 25
GuardPLC Central Functions Chapter 2
Self-test Routines
The most important self-test routines for the safety GuardPLC
controller’s central processing unit and the interface to the I/O level
are described in the following sections.
Microprocessor Test
The following items are checked during the microprocessor test.
•
All used commands and addressing modes
•
Write condition of the flags and the commands controlled by
flags
•
Write condition and the cross-linking of the registers
Test Memory Sectors
The operating system, the application program, the constants and
parameters, and the variable data are stored in every central
processing unit in both processor sectors and are tested by a hardware
comparator.
Fixed Memory Sectors
The operating system, application program, and parameter sector are
each filed in one memory. They are secured by write-protection and a
CRC test.
RAM Test
The RAM sectors, particularly stuck-at and cross-coupling, are tested
with a Write/Read test.
Watchdog Test
The watchdog is switched off if it is not triggered by the two CPUs
within a defined time window. The same applies if the test of the
hardware comparators fails. A separate test determines whether the
watchdog signal is able to switch off.
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