BT8954 CONEXANT [Conexant Systems, Inc], BT8954 Datasheet - Page 36

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

3.0 Circuit Descriptions
3.5 PCM Formatter
3-14
3.5 PCM Formatter
The PCM formatter shifts out the PCMR data at the rising edge of PCMCKI,
samples the PCMT data at the falling edge of PCMCKI, and generates the PCM
frame SYNC signals based on the PCM Format Configuration register [0xF1] as
illustrated in
popular PCM codecs. Because the formatter generates only one frame SYNC
signal for each PCM codec, codecs like the Texas Instruments TP3054A that have
two frame SYNC signals (FSX for transmit and FSR for receive) must have both
frame SYNCs tied before being connected to the Bt8954.
Figure 3-12. PCM Formatter Detail
the COMPRESSED bit configuration in the PCM Format register [0xF1.5]. Only
2:1 ADPCM compression is allowed. Therefore, a 64 kbps time slot is carrying
either 2 x 32 kbps of compressed voice or 64 kbps or clear voice. The Bt8954 has
a maximum capacity of 18 clear or 36 compressed voice channels.
ENC_FSYNC bit configuration in PCM_FORMAT [0xF1.6]. If ENC_FSYNC is
reset, the PCM formatter can generate up to 18 frame SYNCs (PCMF[18:1]). In
this case, the frame SYNCs of all the unused time slots are held low. For example,
for a PCM4 system, PCMF[4:1] are active but PCMF[18:5] are held low.
Encoded_Frame_SYNC mode, driving the channel numbers through
EPCMF[6:1], but holding PCMF[18:7] low. Externally, decoders can be used to
generate frame SYNCs from the channel numbers.
PCMCKI period, while the period for compressed channels is 4 times the
PCMCKI period.
All time slots carry clear voice or compressed voice channels depending on
The frame SYNCs are in an encoded or decoded form depending on the
If ENC_FSYNC is set, the PCM formatter generates the frame SYNCs in the
The period of PCMF[18:1] or EPCMF[6:1] for clear channels is 8 times the
Figure
RFIFO
TFIFO
PCM
PCM
Conexant
3-12. The PCM formatter supports direct connection to
ADPCMCK
PCMR
PCMCKO
PCMCKI
PCMF[18:1]
PCMT
Voice Pair Gain Framer
N8954DSC
Bt8954