2.0 Circuit Description
2.11 Loopbacks
Bt8370/8375/8376
Fully Integrated T1/E1 Framer and Line Interface
2.11 Loopbacks
Bt8370/8375/8376 provides a complete set of loopbacks for diagnostics,
maintenance, and troubleshooting.
2.11.1 Remote Line Loopback
The remote line loopback loops the RCVR inputs to the XMTR outputs. The
loopback provides BPV transparency and the ability to override the looped data
with AIS. The RCVR data path is not affected by the activation of this loopback.
Remote line loopback is activated by setting the Remote Line Loopback
(LLOOP) bit in the Loopback Configuration register [LOOP; addr 014]. It is
possible to operate the remote line loopback simultaneously with the local framer
loopback. If receive jitter attenuator is also enabled, RJAT is placed in the line
loopback path. TJAT, if enabled, is not present in the line loopback path.
2.11.2 Remote Payload Loopback
The remote payload loopback loops all DS0 channels from the RCVR input to the
XMTR output. Loopback payload retains time slot integrity, such that numbered
time slots from each receive frame are transferred to same numbered time slots in
the transmit frame. Transmit overhead bits—F-bits in T1 mode or TS0 in E1
mode—are supplied by the transmit frame formatter or by the TSB, depending on
TFRM [addr 072] settings. Existing transmit frame alignment and clock timing
are not altered by [PLOOP; addr 014] activation or deactivation, allowing system
operation with independent receive and transmit timing. Controlled frame slips
are performed in the payload loopback path if receive and transmit clocks are
asynchronous, although these slips are not reported to the processor as slip buffer
errors. Multiframe integrity is not maintained during PLOOP; therefore, DS0 and
signaling channel loopbacks [TPCn; addr 100–11F] must be used to implement
payload loopback if transparent or forced signaling is desired. PLOOP does not
override by transmit per-channel remote loopback selection (TLOOP bit in
TPCn).
2.11.3 Remote Per-Channel Loopbacks
The remote per-channel loopback loops the RCVR input DS0 channel to the
XMTR output DS0 channel. The remote per-channel loopback is activated by
setting TLOOP in the Transmit Per-Channel Control register [TPC0 to TPC31;
addr 100 to 11F].
2-86
Conexant
N8370DSE
CONEXANT [ CONEXANT SYSTEMS, INC ]
