Motorola APX 4000, Basic Service Manual, Page: 43 / 526

Basic Theory of Operation : Digital (ASTRO) Mode of Operation 3-9
3.3 Digital (ASTRO) Mode of Operation
In the ASTRO (digital) mode of operation, the transmitted or received signal is limited to a discrete
set of frequency deviation levels. The receiver handles an ASTRO-mode signal identically to an
analog-mode signal, up to the point where the DSP decodes the received data. In the ASTRO
receive mode, the DSP uses a different algorithm to recover data.
In the ASTRO transmit mode, microphone audio is processed identically to an analog mode, with the
exception of the algorithm the DSP uses to encode the information. Using this algorithm, transmitter
FM deviation is limited to discrete levels.
3.4 Controller Section
The controller section ( See Figure 3-11. ) comprises of five functional sections that are split among
two boards, which are the main and keypad boards. The main functional section consists of a dual
core ARM and DSP controller, an encryption processor (MACE), Flash memory, and a Double Data
Rate Synchronous Dynamic Random Access Memory (DDR SDRAM) and CPLD for GPIO expander
multiple clock generation and SSI interface for the radio system. The Power and Clocks section
includes a power management IC (MAKO) and various external switching regulators, and three clock
sources (12 MHz and 24.576 MHz) from which all other controller digital clocks are derived. The
Audio section has a CODEC and a class-D audio power amplifier that provides the radio with a
microphone and speaker design. The User Interface section provides communication and control to
the main Liquid Crystal Displays (LCD) on the radio, as well as a keypad and a side connector
interface conforming to GCAI (Global Communications Accessory Interface) specifications. The GPS
and Bluetooth section comprises of a Global Positioning Satellite(GPS) and Bluetooth combo chipset
on the main board, and an AVR Bluetooth controller IC, SDRAM, LF wakeup IC and Accelerometer
IC on the keypad board. The MACE IC is located on the keypad board.
Figure 3-11. Controller Block Diagram
Battery Supply
POWER & CLOCKS
Voltage Regulators
USER INTERFACE
BT,GPS and Encryption
Encryption Processor
Flash Memory
DDR Memory
ARM Processor
Digital Signal Processor
CONTROLLERS & MEMORY
AUDIO
Data Microphone
Audio PA/ Speaker
Main Microphone
Acc. Speaker
Acc. Microphone
Clock sources:
12MHz,
24.576Mhz,
32.768kHz
Main Display
Keypad
Side connector
Top Controller
Keypad Board (full version)
MACE
Bluetooth
Accelerometer
GPS (on main board)
Transceiver