SA2030 Datasheet, PDF (4/12 Pages) Sames – PCM FRAME ALIGNER

SA2030
ALARM SUBSYSTEM
The alarm system may be used by the host equipment to determine the operation status
of the SA2030. The SA2030 provides a bidirectional alarm-port interface DB1 and DB2.
The direction of the interface is controlled by the R/W line. Transfers to or from the
interface are enabled by strobing the port-enable (PE) input. The circuit includes two 2-
bit alarm registers. The four flags in these registers are set when:
- Incoming Alarm-Indication-Signal is received (AIS)
- Loss of frame synchronisation occurs (SYLOSS)
- A distant alarm is received (DISAL)
- A frame slip occurs (SLIP)
* The algorithm used for detection of incoming AIS is in accordance with CCITT
recommendation G.737. That is, AIS will be correctly detected, even in the presence
of random errors, at a rate of 1 in 10³.
* The loss of frame synchronisation flag is set if loss of frame-alignment occurs, if the
route clock is missing or too slow, or if a system-clock-trigger (SCT) pulse is not
applied to the circuit once every alternate frame.
* The distant alarm flag is set if bit 3 of time-slot-zero of frames not containing FAS
is true.
* The frame-slip is set if the frame aligner either drops or repeats a frame.
Selection of which of the two alarm registers is to be read, is carried out by first writing
a command to the comand register via DB1 and DB2. Four commands are supported:
- Enable Read of Alarm Group 1
- Enable Read of Alarm Group 2
- Clear all alarm flags
- Simulate Alarms
Alarm Group 1 includes the AIS and frame synchronisation flags. Alarm Group 2 includes
the Slip and distant alarm flags.
Once an alarm flag is set, it can only be cleared by writing the "clear-all-alarms" command
to the alarm command register. That is, these flags remain set until explicitly cleared.
The simulate-alarm command provides an alarm system self-test capability. This
command simulates all alarm conditions at their sources. If the circuit is operating
correctly, all alarm flags should be set after issuing this command. Alarm simulation tests
the loss of synchronisation function of the frame alignment state-machine, and the AIS
detection logic, and thus may require up to four-frames to complete. After all of the alarm
flags are set, alarm simulation is disabled, and the circuit reverts to normal operation.
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