September 5, 2008 6881076C25-E
3-40 Theory of Operation: ASTRO Spectra Plus VOCON Board
When transmitting, the microphone audio is passed from the command board to the MC145483
CODEC (U402), which incorporates an analog-to-digital (A/D) converter to translate the analog
waveform to a data stream. The data is made available to the DSP through the Serial Audio Port
(SAP) of the Patriot IC. In the converse way, the DSP writes speaker data samples to a D/A in the
CODEC (U402) through the SAP. The CODEC (U402) provides an analog speaker audio signal to
the audio power amplifier on the command board.
Figure 3-15. ASTRO Spectra Plus VOCON Board – Vocoder Section
Modulation
Out
Speaker
D/A
ABACUS
Interface
Mic
A/D
PATRIOT
U300
FLASH
U301
2M x 16
Address/Data/
Control
Command Board
Encryption
Board
SRAM
U302
256k x 16
GPIO
SPI
22.5k x 32
SRAM
SSI - BBP
DSP 56600
KRSIC ADDAG CODEC
SSI - SAP
Command
Board
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