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Reliability Systems: A Maintenance Aid
555-233-123 6-6 Issue 4 May 2002
The Duplication Interface circuit packs support serial links that provide for system
access terminal connection, memory shadowing from Active SPE Memory to
Standby SPE Memory, and communication between software on the Active SPE
and the Standby SPE. Four serial links are supported:
1. The serial link from Duplication Interface A to the system access terminal.
2. The serial link from Duplication Interface A to the Maintenance/Tape
Processor in carrier A.
3. The serial link from Duplication Interface A to the Maintenance/Tape
Processor in carrier B.
4. The serial link from Duplication Interface A to Duplication Interface B.
NOTE:
The Duplication Interface B circuit pack does not communicate directly with
either Maintenance/Tape Processor or with the G3MT.
Duplication Interface A supports the serial channel to the G3MT that is connected
to the Duplication Interface A circuit pack by a connector on the back of carrier A
labeled “DOT” (Duplication Option Terminal). If the Duplication Interface A circuit
pack becomes defective, and the B carrier becomes the Active SPE, the terminal
can be connected to the Maintenance/Tape Processor in carrier B by connecting
the terminal to the connector labeled "TERM" on the back of carrier B. If the
Duplication Interface A circuit pack becomes defective and carrier A becomes the
Active SPE, the terminal can be connected to the Maintenance/Tape Processor in
carrier A by connecting the terminal to the connector labeled "TERM" on the back
of carrier A.
Communication between software on the Active SPE and the Standby SPE is
conducted via a message flow between the two Processors. The flow of
messages from the Processor in carrier A to the Processor in carrier B is as
follows: Processor A to Maintenance/Tape Processor A over the serial link to
Duplication Interface A over the serial link to Maintenance/Tape Processor B to
Processor B. The flow in the reverse direction is exactly opposite.
The serial link between Duplication Interface A and Duplication Interface B is
involved only in memory shadowing from the Active SPE to the Standby SPE as
described in the
‘‘Memory Shadowing’’ section.
SPE Select Switches
The SPE-SELEC (SPE Select) switches are located on the TN772 Duplication
Interface circuit packs and are used to hard-select the Active SPE in a high or
critical reliability system. “Hard-select” means that the SPE Select switches can
be moved from the AUTO position to force the current Active SPE to remain the
Active SPE or to force the current Standby SPE to become the Active SPE. Hard
selection of the Active SPE using the SPE Select switches overrides any attempts
by the system software to switch to the Standby SPE to make it become the
Active SPE.