Rx Signal Path; Figure 3-8. Vocon Board - Vocoder Section - Motorola ASTRO Digital Spectra Plus Detailed Service Manual

3-18
When transmitting, the microphone audio is passed from the command board to the ADSIC, which
incorporates an analog-to-digital (A/D) converter to translate the analog waveform to a series of
data. The data is available to the DSP through the ADSIC parallel registers. In the converse way, the
DSP writes speaker data samples to a D/A in the ADSIC, which provides an analog speaker audio
signal to the audio power amplifier on the command board.
U402
8Kx24
SRAM
U403
8Kx24
SRAM
U414
8Kx24
SRAM
U404
256Kx8
FLASH
3.3.4

RX Signal Path

The vocoder processes all received signals digitally. This requires a unique back end from a
standard analog radio. This unique functionality is provided by the ABACUS II IC with the ADSIC
(U406) acting as the interface to the DSP. The ABACUS II IC located on the RF board provides a
digital back-end for the receiver section. It provides a digital output of I (In phase) and Q
(Quadrature) data words at 20 kHz sampling rate through the ADSIC interface to the DSP. Refer to
the appropriate transceiver section for details on ABACUS II operation.
The ADSIC interface to the ABACUS II is comprised of the four signals SBI, DIN, DIN*, and ODC
(refer to Figure 3-9 on page
September 5, 2008
A0-A15
D0-D23
BUS
CONTROL
Gata Array System
Logic Clock
General
U406
Purpose I/O
ADSIC
Speaker Microphone
D/A A/D
Figure 3-8. VOCON Board – Vocoder Section
3-19).
Theory of Operation: ASTRO Spectra VOCON Board
Host
Port
U405
DSP56001
SCI
Encryption
SERIAL
SSI
SERIAL
Tx D/A
ABACUS Rx
Interface
Serial
HC11
Config.
SPI
HC11/DSP
Interface
Interface
Modulation
Out
ABACUS
Interface
Command
Board
MAEPF-25106-O
6881076C25-E