R e t u r n Channel Modem
D i g i t a l E n t e r t a i n m e n t
O V E R V I E W
Based on DVB-RC, DAVIC, and MCNS
specifications, the VES1848 Return
Channel Modem provides communi-
cation between set-top boxes or
cable modems and the head-end.
The VES1848 integrates seamlessly
with other components of the Vi S TA
solution for set-top box design,
including the VES1820 DVB-C
channel receiver and the VES1900
MCNS QAM re c e i v e r.
The DAVIC/MCNS upstream modu-
lator is built around a digital burst
QPSK or 16QAM modulator. It is
highly programmable, with dire c t l y
p rogrammable IF synthesis, or I and
Q base-band outputs.
Implemented the chip are MAC
i n t e rface and application layer
i n t e rface circ u i t ry, as well as MPEG
t r a n s p o rt stream PID filtering and
re t u rn path frame synchro n i z a t i o n
c i rc u i t ry.
For the downstream channel, the
VES1848 implements a diff e re n t i a l
QPSK demodulator (out-of-band
demodulation) and accepts MPEG2
t r a n s p o rt stream inputs from a down-
s t ream QAM demodulator (in-b a n d
demodulation). The d o w n s t re a m
channel is synchronized with the up-
s t ream channel and provides data to
the MAC layer, which remains extern a l .
F E A T U R E S
Fully compliant with ETS 300 800,
D AVIC 1.1, 1.2
Out-of-band demodulation:
DQPSK demodulator
Roll-off factor
= 0.3
Direct IF sampling
Variable bit rate 1 to 12 MB
(SAW @ 8MHz BW)
Descrambler
Frame synchronization
Deinterleaver
RS decoder (55, 53)
ViSTA VES1848
B l o c k D i a g r a m
Fixed
IF
Out-of-Band
In-Band
Upstream
VES1848
MPEG2-TS
Symbol
Clock
Programmable
IF
I
or
Q
ADC
DQPSK
Demodulator
Channel
Decoding
QPSK/16QAM
Burst Modulator
DACs
Channel
Encoding
PID
Filtering
Frame
Synchro
External
Synchro
MAC Interface
Application Layers
ADC
DQPSK
Demodulator
Channel
Decoding
QPSK/16QAM
Burst Modulator
DACs
Channel
Encoding
PID
Filtering
Frame
Synchro
External
Synchro
MAC Interface
Application Layers
In-band demodulation:
Parallel/serial MPEG2 inputs
PID filtering
ATM transmission supported
Upstream modulation
Burst QPSK/16QAM modulator
R o l l - o ff factors a = 0.25/0.3
P rogrammable U.W. value
P rogrammable burst length
D i rect IF synthesis from
5 to 45 M H z
I and Q base band outputs
Variable bit rate from
256 KB/s to 16 MB/s
P rogrammable RS encoder
S c r a m b l e r
MCNS encoding
Phy layer MAC functionality
CMOS 0.35m technology
208 pin MQFP package
I N T E R F A C E S P E C I F I C A T I O N S
MPEG2 transport stream
i n t e rface (in-band):
8-bit data bus
Byte clock
Symbol clock
P S Y N C
Non-50% duty cycle clock
s u p p o rt e d
IF input (out-of-band):
P rogrammable IF input:
IF = 1.25/n Fsys with
1
n
8 and
Fsys max = 115MHz
Analog or 7-bit input
IF output
F rom 5 to 45MHz (<Fsys/2.5)
Spurious : = -75dBc
10-bit output at Fsys
Analog output
T y p i c a l A p p l i c a t i o n
Baseband output signals
I and Q bit outputs intern a l l y
sampled at Fsys
Analog output
MAC interf a c e
B i d i rectional 8-bit data bus
Chip select
I n t e rrupt line
C l o c k
A d d ress lines (8)
Host interface strobe mode
( I n t e l / M o t o ro l a )
Host interface Mux mode
A d d ress latch enable
R / W
Upper layers interface UTOPIA
reconfigurable into a 16-bit
standard microcontroller i n t e rf a c e
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San Jose, CA 95131
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does not in any way extend or modify VLSI's warranty on any
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products and specifications at any time and without notice.
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1998 VLSI Technology, Inc. Printed in Germany. Document Control: P B - Vi S TA VES1848 V1.0 August 98
Cable
Fixed IF
Fixed IF
Upstream
I Q
Programmable IF
Downstream
Out-of-Band
MPEG2-TS
Tuner
Splitter
Diplexer
VES1820/
VES1900
QAM Demod
Tuner
VES1820/
VES1900
QAM Demod
VES1848
VES2700/
VES6100
MPEG Decoder
and Transpor t
Application Layers
M i c ro c o n t ro l l e r
M A C
Splitter
Diplexer
VES1820/
VES1900
QAM Demod
Tuner
VES1820/
VES1900
QAM Demod
VES1848
VES2700/
VES6100
MPEG Decoder
and Transport
Application Layers
M i c ro c o n t ro l l e r
M A C
PDF 
ZIP