Audio Power Amplifier Steering - Motorola ASTRO XTS 3000 Service Manual

To/From
Vocoder
Board
6-4
specific information and radio personality features. The FLASH ROM
contains the programs which the HC11F1 executes. The FLASH ROM
allows the controller firmware to be reprogrammed for future software
upgrades or feature enhancements. The SRAM is used for scratchpad
memory during program execution.
The SLIC (U702) performs many functions as a companion IC for the
MCU. Among these are expanded input/output (I/O), memory
decoding and management, and interrupt control. It also contains the
universal asynchronous receiver transmitter (UART) used for the
RS232 data communications. The SLIC control registers are mapped
into the MCU's (U701) memory space.
The controller board's audio power amplifier (PA) (U718) is the only
analog IC on the board. This IC is an audio amplifier for the
microphone analog input and speaker analog output. The audio PA
allows steering between the internal and external microphone and
speaker. Steering is accomplished via four control lines provided by the
ADSIC and controlled by the DSP through the ADSIC parallel registers.
Refer to Figure 6-8.
Microphone A/D (MAI)
Speaker D/A (SDO)
General Purpose I/O
Figure 6-8 Audio Power Amplifier Steering
The controller performs the programming of all peripheral ICs. This is
done via a serial peripheral interface (SPI) bus. ICs programmed via
this bus include the synthesizer, DAIC, reference oscillator, display,
and ADSIC. On secure-equipped models, the encryption board is also
controlled through the SPI bus.
In addition to the SPI bus, the controller also maintains two
asynchronous serial busses: the SB9600 bus and an RS232 serial bus.
The SB9600 bus is for interfacing the controller section with different
hardware option boards, some of which may be external to the radio.
The RS232 is functions as a common data interface for external
devices.
User input is handled by the controller through top rotary controls
and side buttons. On models with a display, an additional 3 x 2 (model
II) or 3 x 6 keypad (model III) are also read. User feedback is provided
U718
Audio PA
External
Microphone
Internal
Microphone
External
Speaker
Internal
Speaker
MAEPF-26000-O