BT8954 CONEXANT [Conexant Systems, Inc], BT8954 Datasheet - Page 28

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

3.0 Circuit Descriptions
3.3 Receiver
3.3.2 Receive Framer
Figure 3-4. Receive Framer Finite State Machine
3-6
NO SYNC
OUT_OF
SYNC
SYNC
NO SYNC
NO
SYNC
The receive framer generates the RDSL_6ms pulse after detecting the SYNC
WORD. RDSL_6ms generates pointers that control overhead extraction in the
CRC and OH demux circuitry. The MC initializes the framer to the OUT_OF
SYNC state by writing any data value to SYNC_RST [0xD8]. From the OUT_OF
SYNC state, the framer advances to SYNC_ACQUIRED when the SYNC word is
detected. The framer searches all bits received on RDAT to locate a match with
the SYNC word pattern, SYNC_WORD [0xA1].
RDAT might be inverted. Therefore, the receive framer searches for both the
programmed SYNC word value and the sign-inverted SYNC word value.
Consequently, a maximum of two values of the SYNC word are used in finding
the frame location. If the SYNC word detected is a sign-inverted version of the
configured SYNC word, the framer sets the Tip/Ring Inversion [TR_INVERT]
status bit of the Receive Status 1 register [RSTATUS_1; 0xE5.6] and
automatically inverts the sign of all quats received on RDAT.
state, the framer progresses through a programmable number of intermediate
SYNC_ACQUIRED states before entering the IN_SYNC state. In each
SYNC_ACQUIRED state, the framer searches for the previously detected SYNC
word value in one of two locations based upon the absence or presence of the four
STUFF bits (detected by the STUFF Detector). If the SYNC word is detected in
one of the two possible locations, the STATE_CNT[2:0] counter is incremented
[RSTATUS_2; 0xE6.2:0]. When STATE_CNT[2:0] increments to the value
selected by the REACH_SYNC[2:0] criteria [RCMD_1; 0x90.2:0], the framer
changes to the IN_SYNC state. During the SYNC_ACQUIRED state, if valid
SYNC is not detected at one of the two possible locations, the framer returns to
the OUT_OF_SYNC state as illustrated in
Consecutive SYNC_ACQUIRED states per REACH_SYNC criteria
Consecutive SYNC_ERRORED states per LOSS_SYNC criteria
8
1
Due to the possibility of Tip/Ring connector reversal, all sign bits received on
After detecting the SYNC WORD and changing to the SYNC_ACQUIRED
7
2
6
3
Conexant
5
4
4
5
3
6
2
7
Figure
1
8
3-4.
SYNC
SYNC
Voice Pair Gain Framer
IN_SYNC
SYNC
NO SYNC
N8954DSC
Bt8954