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Technical
Overview
17
The Access Card receives the encrypted keys for decoding a scrambled channel from
the transport
IC. The Access Card deerypts the keys and stores them in a register in
the transport IC. The transport IC uses the keys to decode the data. The Access Card
also handles the tracking and billing for these services
Video data is processed by the MPEG video decoder. This IC decodes the compressed
video data and sends it to the NTSC encoder.
The encoder converts the digital video
information
into NTSC analog video that is output to the S-Video
and standard
composite
video output jacks.
Audio data is likewise
decoded by the MPEG audio decoder.
The decoded
16-bit
stereo audio data is sent to the dual DAC (Digital to Analog Converter)
where the left
and right audio channel
data are separated and converted
back into stereo analog
audio. The audio is output to the left and right audio jacks and is also mixed together
to provide a mono audio source for the RF converter.
The microprocessor
receives and decodes IR remote commands and front keyboard
commands.
Its program
software
is contained
in the processor
ROM (Read Only
Memory).
The microprocessor
controls the other digital devices of the receiver via
address and data lines. It is responsible
for turning on the green LED on the ON/OFF
button.
The modem connects to the customer's phone line and calls the program provider and
transmits the customers programpurchas.es
for billing purposes.
The modem operates
at 1200 bps and is controlled by the microprocessor.
When the modem first attempts
to dial, it sends the first number as touch-tone.
If the dial tone continues after the first
number, the modems switches to pulse dialing and redials the entire number.
If the
dial tone stops after the first number,
the modem continues
to dial the rest of the
number as a touch-tone
number.
The modem also automatically
releases the phone
line if the customer picks up another phone on the same extension.
Thereeeivercontainstwodiagnostictestmenus.
ThefirsttestisacustomercontroUed
Diagnostics
menu that checks the signal, tuning, phone connection and access card. The second
test menu is servicer controlled.
It checks the majority of the receiver for problems.
Customer Controlled Diagnostics
The customer controlled test helps the customer during installation or any time the
receiver appears not to function properly.
Signal test:
Tuning test:
Phone test:
Access card test:
Cheeks the value of error bit number and the error rate to determine
if the antenna connections are properly installed.
Checks to insure a transponder
can be tuned. Thetestis
eousidered
successful and this part of the test is halted if proper tuning occurs
on 1 of the 32 transponders.
The phone
test checks
for dial tone and performs
an internal
loopbaek test.
Sends a message to the access card and cheeks for a valid reply.
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