Bose AV28 Manual page 11

3.2.2 SDRAM
U3 is a 2-megaword by 32-bit synchronous dynamic random access memory (SDRAM) IC. When
the media center powers-up, the application program from the FLASH is shadowed into and ex-
ecuted out of the SDRAM to improve speed. The SDRAM is also used to hold blocks of com-
pressed and decompressed audio and video data, as well as numerous variables and flags, as
required by the software.
For SDRAM accesses, a memory clock of about 100 MHz that synchronizes data access is sent
to the chip at pin 68. Data commands for accesses are coded in the /RAS and /CAS signals (pins
18 and 19), and data read/write selection is done by the /WE signal (pin 17). The address to be
written or read is given on the address bus (pins 25-27 and 60-66). The 32-bit data bus contains
the word to be written or read after the pipeline delay of the memory chip. The detailed operation of
the SDRAM is outside the scope of this document.
3.3 Remote control
3.3.1 RF Transceiver
See sheet 2 of SD256131.
The AV28 media center RF transceiver operates at 27.145 MHz using on-off keying (OOK). The
RF transceiver circuits are located on the Tuner PCB. The antenna for the RF transceiver system
is the DC power cord attached to J104; a 10mH inductor in the power pack facilitates transmission
and reception over the zip cord. The RF signal is capacitively coupled to the V_RAW line by C214.
3.3.1.1 Receiver
The remote control receiver module is an AM receiver; it takes the RF signal from the antenna line,
demodulates it, and outputs the received data to the data slicer circuit. U104, an LM393 dual
comparator, acts as a data slicer and outputs TTL-level signals for the received data waveform.
The RF_DATA_RCV output line connects to U1 through J103.
3.3.1.2 Transmitter
The AV28 media center contains a transmitter for future bidirectional remote control operation.
Q202 and Y201 form a crystal oscillator that is powered when the XMIT/RCV_SEL line from U1 is
high. The output of the oscillator is fed to Q205, a Class-C RF amplifier. Data is sent on the trans-
mitter by way of the RF_DATA_XMIT line from U1, which powers the amplifier. The amplifier's
output is fed through a tank circuit and the filtering network.
3.3.1.3 Filtering network
Passive components on the V_RAW line provide filtering for the RF remote signal: L203, C218, and
C217 form a 27.145 MHz notch; L205, C219, and C216 form a 45.290 MHz (second harmonic of
27.145 MHz) notch. C222, C223, and C224 aid in limiting undesired radiated emissions. FB1 is a
ferrite bead designed to improve tuner performance by limiting radiated self-noise in the FM band.
Theory of Operation
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