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参数资料
| 型号： | AT76C651 |
| 厂商： | ATMEL CORP |
| 元件分类： | 消费家电 |
| 英文描述： | Digital Reception/Transmission Integrated DVB compliant QAM Demodulator(兼容DVB的正交振幅调制解调电路) |
| 中文描述： | SPECIALTY CONSUMER CIRCUIT, PQFP100 |
| 封装： | TQFP-100 |
| 文件页数： | 22/37页 |
| 文件大小： | 497K |
| 代理商： | AT76C651 |
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AT76C651
22
Configuration and Monitoring Registers
Description
The AT76C651 device is controlled by an I
2
C interface.
Most internal registers are in read/write mode (configura-
tion registers). However, monitoring registers are in read-
only mode. Note also that two special registers are write-
only: SETAUTOCFG and RESTART. In most applications,
very few of these registers need to be configured since the
SETAUTOCFG can be used. Some registers are not
described in this document. They are used internally and
should not be written with a different value after SETAU-
TOCFG; otherwise performance degradation may result.
This means that no other address than the ones specified
in this document should be used in I
2
C write mode. Also,
reserved bits in a register should always be written with the
value 0.
General Registers
SYMRATE: 0x00 to 0x02 (read/write)
Transmission symbol rate, f
SYMBOL
, registers give the initial
symbol rate of the timing recovery algorithm. A maximum
offset of 4000 ppm between the actual symbol rate and this
value can be tolerated by the device. The internally com-
pensated frequency offset can be monitored in the register
TIMFREQOFF.
The symbol rate is given as a fraction of the REFCLK fre-
quency. The value must be given with a mantissa (21 bits)
and an exponent (3 bits).
b7
b6
b5
b4
To compute these values, the following equations can be
used:
with
f
REF
2
Example:
For a 30 MHz crystal and pllctrl = 5, f
REF
= 75 MHz
A symbol rate of 5M bauds gives:
exponent = 6 (0x6)
mantissa = 1 118 481(0 x 11 11 11)
So the register value is 0x 88 88 8E.
A symbol rate of 6.875M bauds gives:
exponent = 6 (0x6)
mantissa = 1 537 911(0 x 17 77 77)
So the register value is 0 x BB BB BE (default value).
QAMSEL: 0x03 (read/write)
Specifies the used modulation scheme. This register indi-
cates the number of QAM levels and other parameters
such as the used mapping type (DVB or others), whether
coherent demodulation or differential demodulation is used
for QPSK, and whether intermediate frequency (IF) or
baseband (BB) input is used.
b7
b6
b5
b4
iforbb: 0 for IF input signal, 1 for BB input signal
demtyp: 0 for coherent demodulation, 1 for differential
demodulation (in QPSK only)
maptyp: 00 for DVB mapping, 10 for DAVIC mapping,
other values reserved
qamtyp: Number of bits to specify a QAM symbol.
Example:
2 for QPSK, 4 for QAM-16, 5 for QAM-32,
6 for QAM-64, 7 for QAM-128, 8 for QAM-256,
9 for QAM-512, 10 for QAM-1024 (0, 1, 3, and greater
or equal to 11 are reserved values.)
mantissa (20:13)
0x00
mantissa (12:5)
0x01
mantissa (4:0)
exponent (2:0)
0x02
b3
b2
b1
b0
-------------
pllctrl
=
pllctrl
2 4
,
5
,
6 7
,
,
=
exponent
10
floor
2
log
f
f
REF
----------------
+
=
mantissa
f
f
REF
----------------
2
30
onent
exp
–
=
ifor
bb
dem
typ
maptyp
qamtyp
0x03
b3
b2
b1
b0
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