Bose BUILT-INvisible TA-1 Service Manual page 11

Digital Signal Processor (DSP) PCB (continued)
Microcontroller (continued)
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to sequence the amplifier and codec mute lines as required.
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to boot and monitor the performance of the DSPs.
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and relay information to/from DSPs.
In detail:
1. SmartSpeaker commands are interpreted by watching for digital activity on the serial data
input line (J5, pin 12 [sheet 1, C8]). This serial input can be either the "standard" SmartSpeaker
protocol, compatible with the outputs of CD-5, CD-20, etc., or it can be 4800 baud RS232 with
5V logic levels. The microcontroller decides which protocol to use based on the voltage level
present on the serial data input at boot time. If the line is low, it assumes RS232; if the line is
high, it assumes SmartSpeaker. It checks only once, at boot time, so switching from one proto-
col to the other requires a power cycle to reboot the system.
2. Test mode commands are special commands to facilitate testing, or to retrieve stored informa-
tion from the nonvolatile memory. Test mode commands are RS232 only, e.g., the revision of the
firmware can be queried by sending the command "tv", the answer "2200/2000" might come
back on the serial data output line. This would indicate version 22.00 for the microcontroller and
version 20.00 for the DSPs.
3. The nonvolatile memory is used to store the following information:
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choice of equalization curve.
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system, center, and surround volume settings at power-down.
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US or Euro bass tone control preference.
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system usage statistics.
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number of times system was powered off.
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minutes spent powered on.
4. The codec U100 [sheet 1, C4] has a fair number of internal registers, all of which must be set
up properly for correct operation, e.g., to switch between the ADC inputs and the S/PDIF input
(both functions are integrated into the codec), the codec must be reprogrammed. In addition,
there are a number of error status bits which are periodically sampled by the microcontroller, the
codec can be rebooted if problems are discovered.
5. The tone control potentiometers are not used on the Digital BUILT-INvisible
bass and treble are adjusted by means of pulse width modulation as acheived with the I/O board
microcontroller and support circuitry. See the I/O board theory of operation for a complete
description. The DSP microcontroller has several ADC inputs, two of which are used to detect
the voltage used to adjust the bass and treble. Everytime this voltage changes it is presented to
the DSPs, which adjust their tone control filter coefficients accordingly.
THEORY OF OPERATION
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amplifier. The