module 3BSE066485R1

module 3BSE066485R1

module 3BSE066485R1

If the primary unit fails because of an error, the backup unit resumes execution from the last rollback point, which means the last execution unit is partially re-executed by the backup unit. In order to re-execute a portion of the execution unit without affecting the peripheral units (communication units on the CEX-Bus), the peripheral units’ references are also logged between rollback points. During re-execution, the results of the peripheral units’ references, which have already been executed, are used, rather than re-executing them. The results of read operations are retrieved from the log, and write operations pass without execution, since they have already been executed. The peripheral units’ statuses, then, are not affected by the reexecution in any way, except for the time delay which occurs. The RAM included in the processor unit provides an automatic double inverted memory function for detection of arbitrary bit errors in the memory.

• All memory updates are written to both the primary memory and to the inverted memory in parallel.

• At every memory read cycle, the data from tho two memories is compared.

• If there is a mismatch in the data a changeover is forced. The double inverted memory handling is done in hardware and without any delay to the memory cycle time.