BT8954 CONEXANT [Conexant Systems, Inc], BT8954 Datasheet - Page 24

• Manufacturer Part Number: BT8954
• Description: VOICE PAIR GAIN FRAMER
• Manufacturer: CONEXANT [Conexant Systems, Inc]

3.0 Circuit Descriptions
3.2 DSL Frame Format
Figure 3-2. Basic DSL Frame Format
3.2.1 Detailed Frame Structure
3-2
S
q
1
t
S
q
2
t
0 ms
Sync
Word
7Q
1/(32N + 4S + 4) ms
1Q
D
O
H
B
0
1
12x(4N+0.5S)
B
0
2
3.2 DSL Frame Format
The DSL frame is the fundamental data element of the bit streams transmitted and
received by Bt8954 at the DSL interface. It is patterned after the 2 T1, 2 E1, and
3 E1 frame structures.
Each frame has a 6 ms duration and is made up of 48 payload blocks. Each block
contains S number of S-bits (for data signaling) and N number of bytes where N
is the number of PCM time slots. The microcomputer selects the number of S-bits
in the NUM_SBITS [3:0] field of Transmit Command register 2
[TCMD_2; 0x87.5:2] and the N number of PCM time slots in the NUM_
CHAN[4:0] field of the PCM Format register [PCM_FORMAT; 0xF1.4:0]. S-bits
vary from 0 to 8 bits, while N varies from 1 to 18 time slots. Groups of 12 payload
blocks are concatenated, and each group is separated by an ordered set of DOH
(DSL overhead) bits. A 14-bit SYNC word pattern identifies the beginning of the
DSL frame.
used for stuffing. This corresponds to an 8 kbps (48 bits/6 ms) overhead bit rate.
The 2 bits of stuffing are the average number of stuffing bits per frame since the
transmitter alternatively transmits 0 bits of stuffing or 4 bits of stuffing in each
frame.
0-8 Bits 8 Bits
B
1
2
S-Bits
Forty-eight overhead bits are defined in one DSL frame with the last 2 bits
#Quats = 4 x (48N + 6S) + 24 = 192N + 24S + 24
Bit Rate (kbps) = 2 x (192N + 24S + 24) = (64N + 8S + 8)
#Bits = 2 x (192N + 24S + 24)
5Q
D
O
H
B
1
3
Byte1
#Quats = (4N + 0.5S)
B
1
4
#Bits = 2 x (4N + 0.5S)
Byte2
Conexant
DSL Frame
Figure 3-2
6 ms
B
2
4
5Q
Bnn
D
O
H
Byte3
B
2
5
B
2
6
illustrates the basic format of a DSL frame.
B
3
6
Byte_N
5Q
D
O
H
B
3
7
B
3
8
LEGEND:
S-bits = Data Signaling Bits
Bnn = Payload Blocks 1-48
DOH = DSL Overhead
N = # of Voice Channels
Voice Pair Gain Framer
“6-”
B
4
8
1Q
6 ms
S
q
1
t
1Q
S
q
2
t
“6+”
N8954DSC
Sync
Word
Bt8954