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Bose Personalized Amplification System Manuale di risoluzione dei problemi

THEORY OF OPERATION

1.6 Digital Audio

1.6.1 Overview

The PS1 contains a DSP Analog Devices 21065L, U461 [DSP PCB sheet 3, B4] and a one time

programmable micro-controller U342 [microprocessor PCB sheet 2, C3]. The microcontroller

essentially interfaces to all peripherals and communicates the information from/to the peripher-

als to the DSP which contains most of the intelligence of the system. In addition the

microcontroller acts as a watchdog for the DSP, i.e. it will reset the DSP if the DSP chip hangs

up.

1.6.2 Audio Clocking

The audio signal processing is done at 48 kHz which gets created by an internal 12.288 MHz

(= 256*48kHz) oscillator. XTAL431 [DSP PCB sheet 2, B3] and distributed through U434 [B5].

The PS1 can receive SPDIF through the DATA In connector, but this data is received asynchro-

nously to the actual audio data. This is different from most other Bose

products, where the

master clock is derived from a digital input (if it exists).

Digital audio is transported through an I

S interface (Serial data, Bit clock, Left/Right clock).

U386 [DSP PCB sheet 1, C5] (channel 1/2 A/D) generates the bit clock and the Left/Right clock.

These clocks get buffered through U433 [DSP PCB sheet 2, C5] and routed to U385 [DSP PCB

sheet 1, D4] (channel 3/4 A/D), U387 [B4] (D/A), SPORT 1 (serial port 1) of the DSP, and the

SPDIF transmitter U435 [DSP PCB sheet 2, B7] (Crystal 8046).

1.6.3 Digital to Analog and Analog to Digital Converters (Digital)

Both A/D converters (U385/U386) and the D/A (U387) are hardware configured. U386 is config-

ured as a master and U385 as a slave. The DSP can reset the A/D through FLAG3 and the D/A

through FLAG2. The data is received by the DSP on SPORT1 (serial port 1) channel A (U385)

and channel B (U386). The DSP transmits the audio data again on SPORT1 (serial port 1)

channel A (to the D/A, U387) and channel B (SPDIF transmitter, U435).

1.6.4 SPDIF Interface

The SPDIF output provides the unprocessed audio received from channel 1 and 2. It is basically

a digital copy of the input signals to U386. The audio is sent by the DSP through channel B on

SPORT1 in I

S mode and received by U435, a Crystal 8046 SPDIF transmitter. U435 can be

reset by the DSP through FLAG1. U435 generates proper SPDIF signals and these get routed

through a transformer T431, through CN113 back to the Data Out connector on the panel board.

The "Data In" SPDIF input is NOT designed to receive actual audio, but to receive data that is

disguised as a SPDIF bit stream. The SPDIF input is clocked independent from the rest of the

system. The signal is received on the "Data In" connector on the panel board and routed through

CN112 to the DSP board and received by Crystal 8416 SPDIF receiver (U431), which performs

clock and data recovery. The data is transferred through an I

S interface to the DSP and re-

ceived through SPORT0 on channel A. The DSP evaluates the data asynchronously. The DSP

can reset U431 through FLAG0 and can monitor the whether the U431 has valid audio through

FLAG8.