Siemens SIMATIC S7-400H Manual page 36

System and Operating Modes of the S7-400H
Self-tests
Malfunctions have to be detected, isolated and reported as quickly as possible.
Consequently, widely-ranging self-test functions have been implemented on the
S7-400H and run automatically and entirely in the background after POWER ON,
in cyclic operation and even in the ERROR-SEARCH mode.
The following components and functions are tested:
interconnection of the central controllers
processor
memory
I/O bus
The high-quality RAM test is a very special feature. It is processed only after an
unbuffered POWER ON and in the ERROR-SEARCH mode. The test requires
approximately 8 seconds per megabyte of RAM.
Processing self-tests
After an unbuffered POWER ON (for example, POWER ON after plugging in the
CPU for the first time or POWER ON without a back-up battery) and in
ERROR-SEARCH mode, the CPU executes the complete self-test program. The
processing time of the full self-test depends on the configuration of the S7-400H
and lasts approximately 30 to 90 sec.
At RUN the operating system divides the self-test into small program sections (test
slices) that are processed consecutively over a whole number of cycles. The
self-test is organized so that it runs once to the end within 90 minutes. (The 90
minutes are a default value which you can modify by configuring.)
If an error is found as a result of the self-test, the following happens:
In the event of a hardware error, the CPU enters the cause of the error in the
diagnostic buffer and goes to the "Defective" mode.
In the event of a RAM/PAA comparison error the cause of the error is entered in
the diagnostic buffer and the configured system or operating mode is entered.
The master CPU continues to operate at Solo mode.
Influencing the cyclical self-test
With the SFC 90 H_CTRL You can also affect the scope and execution of the
cyclical self-test. For example, you can remove and replace individual components
of the test. In addition, certain test components can be explicitly called and started
for execution.
You will find detailed information on the SFC 90 H_CTRL in the manual on System
Software for S7-300/400, System and Standard Functions .
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S7-400H Programmable Controller Fault-Tolerant Systems
A5E00068197-04