Bt8370/8375/8376
2.0 Circuit Description
2.4 Receiver
Fully Integrated T1/E1 Framer and Line Interface
The offline framer is shared between the RCVR and XMTR and can search in
only one direction at any time. Consequently, the processor arbitrates which
direction is searched by enabling the reframe request (RLOF and TLOF) for that
direction.
The offline framer waits until the current search is complete (see [FSTAT; addr
017]) before checking for pending LOF reframe requests. If both online framers
have pending reframe requests, the offline framer aligns to the direction opposite
from that which was most recently searched. For example, if TLOF is pending at
the conclusion of a receive search which timed out without finding alignment, the
offline framer switches to search in the transmit direction. The TLOF switchover
is prevented in the preceding example if the processor asserts TABORT to mask
the transmit reframe request. TABORT does not affect TLOF status reporting. For
applications that frame in only 1 direction, the opposite direction should be
masked. If, at the conclusion of a receive search, TLOF status is asserted but
masked by TABORT, the offline framer continues to search in the receive
direction. For applications that frame in both directions, the processor can allow
the offline framer to automatically arbitrate among pending reframe requests, or
can elect to manually control reframe precedence. An example of manual control
follows:
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Initialize RABORT = 1 and TABORT = 1
Enable RLOF and TLOF interrupts
Read clear pending ISR interrupts
Release RABORT = 0
Call LOF Service Routine if either RLOF or TLOF interrupt;
{
(check current LOF status [ALM1, 2; addr 047, 048]
If RLOF recovered and TLOF lost
—Assert RABORT = 1
—Release TABORT = 0
If RLOF lost or TLOF recovered
—Assert TABORT = 1
—Release RABORT = 0
}
The status of the offline framer can be monitored for diagnostic purposes
using the Offline Framer Status register [FSTAT; addr 017]. The register reports
the following:
•
whether the offline framer is looking at the receive or transmit data streams
(RX/TXN)
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•
•
•
whether the framer is actively searching for a frame alignment (ACTIVE)
whether the framer found multiple framing candidates (TIMEOUT)
whether the framer found frame sync (FOUND)
whether the framer found no frame alignment candidates (INVALID)
NOTE: These status bits are updated in real time and might be active for only very
short (1-bit) periods of time.
N8370DSE
Conexant
2-25
CONEXANT [ CONEXANT SYSTEMS, INC ]
