BT8954 Datasheet, PDF (1/98 Pages) Conexant Systems, Inc – VOICE PAIR GAIN FRAMER

Bt8954
Voice Pair Gain Framer
The Bt8954 framer has been tailored specifically to meet the needs of voice pair gain
systems (also referred to as “cable relief systems” and “digital subscriber line carriers”)
by providing a direct connection to the DSL modem and the CODEC. It performs data,
clock, and format conversions necessary to construct a Pulse Code Multiplexed (PCM)
channel from a Symmetrical Digital Subscriber Line (SDSL) or a High-Bit-Rate Digital
Subscriber Line (HDSL) channel. The PCM channel consists of transmit and receive
data, clock, and frame sync signals configured for 2–18 voice channels. The PCM
channel connects directly to popular PCM codecs. The Digital Subscriber Line (DSL)
channel interface consists of serial data and clock connected to a RS8973, Bt8970 or a
Bt8960 DSL Transceiver. The Bt8954 supports clear and compressed voice system.
When coupled with a Bt8960, the Bt8954 provides PCM4 functions at greater than 5 km
reach with no voice compression, allowing V.34 modem operation.
At one end, Bt8954 multiplexes payload data from several PCM codecs with the
appropriate overhead and signaling bits into one transport frame that is passed on to the
bit-pump, for transport over a single twisted pair. At the other end, Bt8954
demultiplexes the DSL bit stream into payload data sent to the PCM codec, and
overhead data written into microcomputer-accessible registers.
Embedded Operations Channel (EOC) and signaling overhead can be inserted via the
Microcomputer Interface (MCI). Control and status registers are accessed via the MCI.
One common register group configures the PCM interface formatter, Phase-Locked
Loop (PLL), and PCM Loopback (LB). Another group of DSL channel registers
configures the elastic store FIFOs, overhead muxes, receive framer, payload mapper, and
the DSL loopback. Status registers monitor received overhead, PLL, FIFO, and framer
operations, including CRC and FEBE error counts.
Functional Block Diagram
RDAT
HCLK
BCLK
QCLK
TDAT
Receive
Framer
2B1Q
Decoder
Payload
Demux
PCM
RFIFO
OH/Signaling
LB
PLL
Registers
LB
2B1Q
Encoder
Payload
Mux
PCM
TFIFO
Microcomputer Interface
PCMR
ADPCMCK
PCMCLK
PCMF[18:1]
PCMT
Distinguishing Features
• Voice Pair Gain Framer
– Frames and transports PCM data
streams over 12–18,000 ft.
(3.7–5.5 km) distances when
coupled with Bt8960 or Bt8970
• PCM Interface
– Supports popular PCM codecs
– Programmable payload to
support 2–18 64 kbps voice
channels
– 2.048, 1.536 MHz PCM reference
clock generation
– 6.144, 8.192, 20.48 MHz ADPCM
reference clock generation
• DSL Interface
– Connects to Bt8960 or Bt8970
– Supports 160–1168 kbps bit rates
– Error performance monitoring
– Auto tip/ring reversal
• Microcomputer Interface
– Glueless interface to Intel 8051
and Motorola 68302 processors
– Access to overhead and signaling
registers
• Supports ADPCM codecs (32 kbps)
• PCM and DSL loopbacks
• CMOS technology, 5 V operation
• Low-power operation
– Enables compatibility with
line-powered systems
• 68-pin PLCC
• JTAG/IEEE Std 1149.1-1990
• –40 °C to +85 °C operation
Applications
• Voice Pair Gain Systems (Clear)
– PCM2, PCM4(PCM1+3), PCM6,
– PCM8, PCM10/11, PCM12,
PCM18
• ADPCM Voice Pair Gain Systems
(Compressed)
– ADPCM12, ADPCM24, ADPCM36
Microcomputer
Data Sheet
N8954DSC
April 7, 1999