2.0 Circuit Description
2.7 Transmit System Bus
Bt8370/8375/8376
Fully Integrated T1/E1 Framer and Line Interface
2.7.4 Transmit Framing
The transmit data stream has two framing functions: offline framer and an online
framer. Figure 2-27 illustrates these functions. The offline framer recovers the
transmit frame alignment (TFSYNC). The online framer monitors the frame
alignment found by the offline framer and recovers multiframe alignment
(TMSYNC).
Transmit frame resynchronization is initiated by activating the Transmit Loss
of Frame (TLOF) status bit in Alarm 2 status [ALM2; addr 048] register by the
online framer. The TLOF criteria is set in the TLOFA, TLOFB, and TLOFC bits
of the Transmitter Configuration register [TCR1; addr 071]. The online framer
supports the following LOF criteria for T1: 2 frame bit errors out of 4; 2 out of 5;
or 2 out of 6. For E1, it supports 3 out of 3.
Figure 2-27. Transmit Framing and Timebase Alignment Options
TSLIP
Buffer
TNRZ
TPCMI
TPHASE
CAS MFAS
Online Online
Recenter
(TUSLIP)
01
C
A
Offline
Framer
TFSYNCI
TMSYNCI
Pass
MF
TSB
Offset
B
D
FSYNC FAS CAS MSYNC
TX Timebase
FSYNC MSYNC
TSB Timebase
TFSYNCO
TMSYNCO
Pass
MF
TX Aligns to TNRZ (EMBED = 1)
TX Aligns to TSB (TX_ALIGN = 1)
C
D
TSB Aligns to TPCMI (EMBED = 0)
A
B
TSB Aligns to TX (TSB_ALIGN = 1)
(EMBED = 1)
NOTE(S):
1. EMBED located in SBI_CR (addr 0D0).
2. TSB_ALIGN and TX_ALIGN located in TSB_CR (addr 0D4).
3. EMBED = 0 is only applicable if TPCMI is operating at the line rate.
When TLOF is asserted, the offline framer searches the transmit data stream
for a new frame alignment, provided transmit framing is enabled [TABORT; addr
071]. If embedded framing is enabled [EMBED; addr 0D0], the offline framer
examines the TSLIP buffer output, TNRZ, for transmit frame alignment. If
embedded framing is disabled, the offline framer examines the slip buffer input
(TPCMI) for transmit frame alignment. This case (EMBED = 0) is only applicable
if TPCMI is configured to operate at the line rate: 2,048 kbps E1, or 1,544 kbps
T1. If transmit framing is disabled, the offline framer waits for a reframe command
[TFORCE; addr 071] before beginning frame alignment search.
2-50
Conexant
N8370DSE
CONEXANT [ CONEXANT SYSTEMS, INC ]
