Rainbow Electronics DS31256 - Manual (Page 56)

DS31256
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Bit 14/Route Data from BERT (TBERT). Setting this bit routes DS0 data to the TD pin from the BERT block
instead of from the HDLC controller. If the DS0 channel has been configured for 56kbps operation (T56 = 1), the
LSB of each DS0 channel is not routed from the BERT block but instead is forced to 1. In order for the data to
make it from the BERT block, the host must also configure the BERT for the proper port through the master
control register (Section
5 ). This bit overrides TFAO and TCHEN.
0 = do not route data from BERT
1 = route data from BERT (override the data from the HDLC controller)
Bit 15/Transmit DS0 Channel Enable (TCHEN). This bit must be set for each active DS0 channel in a
channelized application. In a channelized application, although a DS0 channel is deactivated, the channel can still
be set up to route data from the BERT block. In addition, although a DS0 channel is active, the loopback function
(CNLB = 1) overrides this activation and routes receive data to the TD pin instead of from the HDLC. In an
unchannelized mode (TUEN = 1), only the TCHEN bit in T[n]CFG0 needs to be configured.
0 = deactivated DS0 channel
1 = active DS0 channel
6.4 Receive V.54 Detector
Each port within the device contains a V.54 loop pattern detector. V.54 is a pseudorandom pattern that is
sent for at least 2 seconds, followed immediately by an all-ones pattern for at least 2 seconds if the
channel is to be placed into loopback. The exact pattern and sequence is defined in Annex B of ANSI
T1.403-1995.
When a port is configured for unchannelized operation (RUEN = 1), all data entering the port through
RD is routed to the V.54 detector. If the host wishes not to use the V.54 detector, the SLBP status bits in
the status V.54 (SV54) register should be ignored, and their corresponding interrupt mask bits in ISV54
should be set to 0 to keep from disturbing the host. Details about the status and interrupt bits can be
found in Section
5 .
When the port is configured for channelized operation (RUEN = 0), it is the host’s responsibility to
determine which DS0 channels should be searched for the V.54 pattern. In channelized applications, it
may be that there are multiple HDLC channels the host wishes to look in for the V.54 pattern. If this is
true, then the host performs the routine shown in
Table 6-B . A flow chart of the same routine is shown in
Figure 6-5 .