Bt8370/8375/8376
2.0 Circuit Description
2.7 Transmit System Bus
Fully Integrated T1/E1 Framer and Line Interface
After the offline framer recovers frame alignment, the online framer monitors
TLOF and searches for multiframe alignment; the search uses the criteria defined
by the Transmit Frame mode [TFRAME; addr 070]. The online framer conducts a
multiframe alignment search each time the offline framer recovers transmit frame
alignment, as reported by high-to-low transition of transmit loss of frame status
[TLOF; addr 048]. After TLOF recovery, the online framer searches continuously
for multiframe alignment until the correct pattern sequence is located, or until
basic frame alignment is lost (TLOF goes active-high). After multiframe
alignment recovery, the online framer checks subsequent multiframes for errored
alignment patterns, but does not use those errors as part of the criteria for loss of
basic frame alignment.
NOTE: The online framer's multiframe search status is not directly reported to the
processor, but instead is monitored by examination of transmit error status:
TMERR, TSERR, and TCERR [addr 00B]. If the system incorporates a
certain number of multiframe pattern errors (or a certain error ratio) into
the loss of transmit frame alignment criteria, the processor must count
multiframe pattern errors to determine when to force a transmit reframe
[TFORCE; addr 071].
The frame synchronization criteria used by the offline framer is set in the
TFRAME[3:0] of the Transmit Framer Configuration register [TCR0; addr 070].
(Tables 3-15 and 3-16 illustrate supported transmit framing formats. Also, see
Tables 3-17 and 3-18, Criteria for Loss/Recovery of Transmit Frame Alignment.)
The offline framer is shared between the RCVR and XMTR and can only
search in 1 direction at a time. Consequently, the host processor can manually
arbitrate between RCVR and XMTR reframe requests by manipulating the
ABORT and FORCE controls, or by allowing the framer to automatically
arbitrate LOF requests.
The offline framer waits until the current search is complete [FSTAT;
addr 017] before checking for pending LOF reframe requests. If both online
framers have pending reframe requests, the offline framer aligns to the opposite
direction of that 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, framing in the opposite direction must
be masked. If, at the conclusion of a receive search timeout, TLOF status is
asserted but masked by TABORT, the offline framer continues to search in the
receive direction.
N8370DSE
Conexant
2-51
CONEXANT [ CONEXANT SYSTEMS, INC ]
