Siemens SIMATIC CPU 410 System Manual page 116

System and operating states of the CPU 410
7.3 Self-test
Hardware fault with one-sided OB 121 call, checksum error, 2nd occurrence
The response of a CPU 410 to the second occurrence of hardware faults with one-sided OB
121 call and checksum errors is as shown in the following table for the various operating
modes of a CPU 410.
Table 7- 6 Hardware fault with one-sided OB 121 call, checksum error, 2nd occurrence
Error
Hardware fault with one-
sided OB 121 call
Checksum error
If a second checksum error occurs in solo or stand-alone operation after twice the test cycle
time has expired, the CPU reacts as it did on the first occurrence of the error. If a second
error (hardware fault with one-sided OB 121 call, checksum error) occurs in redundant
operation after expiration of the troubleshooting operation, the CPU responds the same as to
the first occurrence of the error.
Multiple-bit errors
If a multiple-bit error is detected during redundant operation of a fault-tolerant system, the
CPU switches to ERROR-SEARCH operating state. When troubleshooting is finished, the
CPU can be linked up and updated again, and resume redundant operation. If there is no
error on the CPU 410, it switches to RUN and becomes the master. The cause of the error is
signaled by the call of OB 84.
There are some rare cases in which multiple-bit and single-bit errors can occur due to very
challenging ambient conditions. If they occur only once, they do not interfere with the
hardware. If bit errors occur frequently, however, replace the hardware.
Single-bit errors
Single-bit errors are also detected and eliminated outside the self-test. After elimination of
the error, the CPU 410 calls OB 84.
Influencing the cyclic self-test
SFC 90 "H_CTRL" allows you to influence the scope and execution of the cyclic self-test. For
example, you can remove various test components from the overall test and re-introduce
them. In addition, you can explicitly call and process specific test components.
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CPU in stand-alone operation/single mode
OB 121 is executed
The CPU enters the DEFECTIVE state if two
errors occur within two successive test cycles
(You configure the length of the test cycle in
HW Config)
CPU in redundant operation
The faulty CPU switches to ERROR-SEARCH
operating state. The fault-tolerant system
switches to stand-alone operation.
The CPU enters the DEFECTIVE state if a
second error triggered by the first error event
occurs in ERROR-SEARCH mode.
CPU 410 Process Automation/CPU 410 SMART
System Manual, 05/2017, A5E31622160-AC