RS8953 Conexant Systems, Inc., RS8953 Datasheet - Page 57

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

RS8953B/8953SPB
HDSL Channel Unit
N8953BDSB
3.5.1.3 CRC Calculation
3.5.1.4 Scrambler
3.5.1.5 STUFF
Generator
The Cyclic Redundancy Check (CRC) calculation is performed on all transmit
data, and the HOH multiplexer inserts the resulting 6-bit CRC into the subsequent
output frame. CRC is calculated over all bits in the (N)th frame except the SYNC,
STUFF, and CRC bits, and then is inserted into the (N+1)th frame. The MPU can
choose to inject CRC errors on a per frame-basis by setting ICRC_ERR
[TCMD_1; addr 0x07]. The six CRC bits are calculated as follows:
The scrambler operates at the BCLKn bit rate on all HDSL transmit data, except
for the 14-bit SYNC words and the four STUFF bits. The MPU enables the
scrambler by setting SCR_EN [TCMD_1; addr 0x06] and selects the scrambler
algorithm in SCR_TAP [TCMD_2; addr 0x07]. Two scrambler algorithms are
implemented for HTU-R or HTU-C data transmission:
Transmit bit stuffing synchronizes the HDSL channel’s transmit 6 ms frame
period to the PCM channel’s 6 ms sync by adding 0 or 4 STUFF bits to the HDSL
output frame. The STUFF generator decides whether 0 or 4 STUFF bits are
inserted and reports the result of each decision in TX_STUFF [STATUS_3; addr
0x07]. When 4 STUFF bits are inserted, sign/magnitude values are taken from
TSTUFF [addr 0xE4]. Stuffing decisions are based on comparison of the phase
difference measured between PCM and HDSL 6 ms frame intervals in relation to
the programmed STUFF thresholds [STF_THRESH_B; addr 0xD1] and
threshold [STF_THRESH_C; addr 0xD3]. If the measured phase difference is
equal to or less than threshold B, then no STUFF bits are inserted for that output
frame. If the measured phase difference exceeds threshold B and is less than or
equal to threshold C, then 4 STUFF bits are inserted. When the measured phase
exceeds threshold C, the STUFF generator reports a transmit Stuffing Error,
STUFF_ERR [STATUS_3; addr 0x07] and automatically resets the transmit FIFO
by performing the TFIFO_RST [addr 0x0D] command.
1.
2.
3.
• In the HTU-R to HTU-C direction, the polynomial shall be
• In the HTU-C to HTU-R direction, the polynomial shall be
All bits of the (N)th frame, except the 14 SYNC, 6 CRC, and any STUFF
bits are used to calculate CRC. A total of 4,682 bits are used, in order of
occurrence, to construct a polynomial in X, such that bit 0 of the (N)th
frame is the coefficient of the term X
is the coefficient of the term X
The polynomial is multiplied by the factor X
modulo 2, by the generator polynomial X
remainder polynomial are used, in order of occurrence, as an ordered set of
check bits, CRC1–CRC6, for the (N+1)th frame. Ordering is such that the
coefficient of term X
the coefficient of term X
Check bits CRC1–CRC6 contained in a frame are associated with the
contents of the preceding frame. When there is no immediately preceding
frame, check bits may be assigned any value.
X
X
–23
–23
X
X
–18
–5
1, where
Conexant
1, where
5
in the remainder polynomial is check bit CRC1, and
is equal to modulo 2 summation.
0
is equal to modulo 2 summation.
is check bit CRC6.
0
.
4681
6
and bit 4681 of the (N)th frame
+X+1. Coefficients of the
6
and the result is divided,
3.0 Circuit Descriptions
3.5 HDSL Channel
3-25