RS8953 Conexant Systems, Inc., RS8953 Datasheet - Page 88

• Manufacturer Part Number: RS8953
• Description: High-bit-rate Digital Subscriber Line (hdsl) Channel unit
• Manufacturer: Conexant Systems, Inc.

4.0 Registers
4.4 HDSL Receive
THRESH_CORR[3:0]
DSCR_TAP
DSCR_EN
PH_LOOP
4-20
0x61—Receive Command Register 2 (RCMD_2)
RX_ERR_EN
7
PH_LOOP
SYNC Threshold Correlation—Upon the receive framer’s entry to a Sync Errored state, the
number of SYNC word locations searched is determined by the result of the previous states’
threshold correlation. During an In Sync state, the framer searches the two most probable
SYNC word locations at 6 ms
locations searched must correctly match the entire 14-bit SYNC word or the framer enters a
Sync Errored state. The highest number of matching bits found among the search locations is
compared to the selected THRESH_CORR value to determine whether the framer should
expand the number of search locations. If the highest number of matching bits meets or
exceeds the threshold, but was not a complete match, the framer progresses to the next Sync
Errored state and continues to each of the two most probable locations. Otherwise, the framer
progresses to the next Sync Errored state, increments the number of locations to be searched,
and examines quats on either side of the prior search locations. For example, if the location
with the highest number of matching bits is below the threshold during In Sync, then the
framer enters the first Sync Errored state and searches from the prior location at 6 ms 2
quats, and at exactly 6 ms. The effect of threshold correlation on the number of search
locations is depicted in
Descrambler Tap—Selects which delay stage, 5th or 18th, to tap for feedback in the
descrambler. The system’s terminal type dictates which tap should be selected.
Descrambler Enable—When enabled, all receive HDSL channel data, except SYNC and
STUFF bits, are descrambled per the DSCR_TAP setting. Otherwise the data passes through
the descrambler unchanged. DSCR_EN also determines whether RSER and RAUXn data are
descrambled.
Loopback to PCM on HDSL Side—Transmit HDSL data (TDATn) is connected back towards
the PCM interface to accomplish a loopback of the PCM channel on the HDSL side. Receive
HDSL data (RDATn) is ignored, but HDSL transmit continues without interruption.
PH_LOOP requires the descrambler and scrambler to use the same tap, as opposed to their
normal opposing tap selection.
6
DSCR_EN
5
0 = HTU-C or LTU terminal type, descrambler selects tap 18
1 = HTU-R or NTU terminal type, descrambler selects tap 5
0 = Descrambler bypassed
1 = Descrambler enabled
0 = Normal receive
1 = RDATn supplied by TDATn
Figure
THRESH_CORR
DSCR_TAP
3-24.
4
1010
1011
1100
1101
1110
1 quat, corresponding to 0 or 4 STUFF bits. One of the two
Conexant
3
SYNC Threshold Correlation
THRESH_CORR[3:0}
2
10 or more out of 14 bits
11 or more out of 14 bits
12 or more out of 14 bits
13 or more out of 14 bits
14 out of 14 bits
RS8953B/8953SPB
1
HDSL Channel Unit
N8953BDSB
0