Motorola ASTRO Digital Spectra, Detailed Service Manual, Page: 75 / 442

6881076C25-E September 5, 2008
Theory of Operation: ASTRO Spectra VOCON Board 3-15
3.3 ASTRO Spectra VOCON Board
This section of the theory of operation provides a detailed circuit description of an ASTRO Digital
Spectra Vocoder/Controller (VOCON) board. When reading the Theory of Operation, refer to your
appropriate schematic and component location diagrams located in
“Chapter 7. Schematics,
Component Location Diagrams and Parts Lists” . This detailed Theory of Operation will help isolate
the problem to a particular component. However, first use the ASTRO Digital Spectra and Digital
Spectra Plus Mobile Radios Basic Service Manual to troubleshoot the problem to a particular board.
NOTE: The information in this subsection applies to the non Plus VOCON board. Refer to Section
3.4, "ASTRO Spectra Plus VOCON Board," on page 3-38 for information on the ASTRO
Spectra Plus VOCON board.
3.3.1 General
The VOCON board consists of two subsystems; the vocoder and the controller. Although these two
subsystems share the same printed circuit board and work closely together, it helps to keep their
individual functionality separate in describing the operation of the radio.
The controller section is the central interface between the various subsystems of the radio. It is very
similar to the digital logic portion of the controllers on many existing Motorola radios. Its main task is
to interpret user input, provide user feedback, and schedule events in the radio operation, which
includes programming ICs, steering the activities of the DSP, and sending messages to the display
through the control head.
The vocoder section performs all tone signaling, trunking signalling, conventional analog voice, etc.
All analog signal processing is done digitally utilizing a DSP56001. In addition it provides a digital
voice plus data capability utilizing VSELP or IMBE voice compression algorithms. Vocoder is a
general term used to refer to these DSP based systems and is short for voice encoder.
In addition, the VOCON board provides the interconnection between the microcontroller unit (MCU),
digital-signal processor (DSP), command board, and encryption board on secure-equipped radios.
3.3.2 Controller Section
Refer to Figure 3-7 on page 3-16 and your specific schematic diagram.
The controller section of the VOCON board consists entirely of digital logic comprised of a
microcontrol unit (MCU-U204), a custom support logic IC (SLIC-U206), and memory consisting of:
SRAM (U202), EEPROM (U201), and FLASH ROM (U205).
The MCU (U204) memory system is comprised of a 32k x 8 SRAM (U202), 32k x 8 EEPROM
(U201), and 512k x 8 FLASH ROMs (U205). The MCU also contains 1024 bytes of internal SRAM
and 512 bytes of internal EEPROM. The EEPROM memory is used to store customer 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.