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參數(shù)資料
| 型號： | MC92305CD |
| 廠商： | Motorola, Inc. |
| 英文描述： | 16/32/64/128/256 QAM RECEIVER AND REED-SOLOMON DECODER |
| 中文描述： | 16/32/64/128/256的QAM接收器和Reed - Solomon解碼器 |
| 文件頁數(shù)： | 3/4頁 |
| 文件大?。?/td> | 39K |
| 代理商： | MC92305CD |
MC92307
Rev.1.1
MOTOROLA
3
PRBS Descrambling
The error corrected data from the Reed Solomon
decoder is de-randomized using a PRBS generator
with polynomial 1 + X
14
+ X
15
. The PRBS generator is
initialized every 8 MPEG transport packets with the val-
ue 100101010000000 as per the DVB specification.
I
2
C Interface
In accordance with the I
2
C specification, the I
2
C
master (host microprocessor) initiates all data transfers
to and from the demodulator and provides the I
2
C
clock. Data is always transferred one byte at a time,
MSB first, and the receiver must acknowledge each
byte by pulling the data line low during the cycle follow-
ing the LSB (acknowledge cycle). The demodulator in-
terprets the byte following its slave address as an 8-bit
sub-address which selects a particular register to be
written to or read from. The I
2
C data pin is bidirectional
and is driven by an open-drain output in the MC92305.
External pull-up resistors are required to implement the
wired-AND function on each of these signals, per the
I
2
C bus specification.
Σ
Interfaces
The single-bit outputs which interface to analog
circuits are VCOOUT, AGCOUT and CTLOUT. These
are the loop filter outputs for the MSS symbol sync,
AGC and Carrier Tracking Loop, respectively. The dig-
ital sigma-delta converters which drive these outputs
have programmable output sampling rates up to a max-
imum of 4.0Rs. The bandwidths of each of these loops
and the output sampling rates of the loops (input sam-
pling rates of the sigma-delta converters) are program-
mable. The sigma-delta output sampling rates should
be commensurate with the loop bandwidths and loop
output sampling rates selected.
Pin-Programmable Interfaces
A variety of functions are selectable by hard-wiring
MC92305 pins to VDD or VSS, rather than via the I
2
C
interface. These fall in the category of functions which
will seldom be changed once a particular application
circuit is debugged and functioning correctly. The pin
programmable features are:
IQSWAP - Swap internal I and Q data paths
IN_FMT - Specify A/D output data format (two’s
complement or offset binary)
SYM_FE - specify which edge of the output symbol
clock is to be aligned with the symbols.
TSTMODE - Used during production testing of the
device but can also be used to disable and bypass
certain of the functions in the MC92305.
Software-Configurable Items
The command interfaces can address a variety of
internal registers to configure most critical demodulator
and decoder parameters. These include: all loop band-
widths, equalizer tap values and equalizer control (load
taps and adapt, load taps and freeze, adapt without
loading and freeze without loading), the filter coeffi-
cients of the receive lowpass filter, the lock detector
thresholds for MSS lock and Carrier lock, the center tap
fixed gain adjustment, the NCO frequency preset, soft-
ware reset (which performs the same function as the
hardware power-on reset), upper and lower limits on
the NCO frequency and, input and output sampling
rates of each digital sigma-delta converter.
Software-Readable Items
All of the software-configurable registers are also
readable. This is intended to allow the host to interro-
gate the demodulator prior to changing parameters.
There are also a number of demodulator registers
which are read-only and are intended to provide useful
demodulator status information to the host for monitor-
ing and debugging purposes. These include: NCO fre-
quency (which provides an indirect measurement of the
frequency error in the channel tuner and modem local
oscillators), AGC control value (an indicator of received
signal power), constellation variance (an indicator of re-
ceived energy per symbol to noise power spectral den-
sity) Es/No, (used in generating the carrier lock detect
signal) and, MSS control value (which provides an indi-
rect measurement of baud rate error and is used in gen-
erating the MSS lock detect signal).
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