February 3, 2003 6881076C20-E
3-8 Basic Theory of Operation: VOCON (Vocoder/Controller) Board
The VOCON board controls receive/transmit frequencies, the display, and various radio functions,
using either direct logic control or serial communication to external devices. The connector J801
provides an interface between the encryption module and the VOCON board for encrypting voice
messages.
The VOCON board executes a stored program located in the FLASH ROM. Data is transferred to
and from memory by the microcontroller unit data bus. The memory location from which data is read,
or to which data is written, is selected by the address lines.
The vocoder circuitry on the VOCON board is powered by two regulated voltage supplies: 3.0 Vdc
and 1.8 Vdc. These regulated supplies are powered by a switched 5 Vdc regulator located on the
command board. This 5 Vdc supply also powers some vocoder circuitry. This voltage is removed
from the board when the radio is turned off by the control head switch.
The DSP Core inside the Dual-Core processor performs signaling, voice encoding/decoding, audio
filtering, and volume control functions. This core performs Private-Line/Digital Private-Line (PL/DPL)
encode and alert-tone generation. The DSP Core transmits pre-emphasized analog signals and
applies a low-pass (splatter) filter to all transmitted signals. The Dual-Core processor requires a
16.8MHz and a 32 kHz clock to function.
The DSP-support ICs perform analog-to-digital and digital-to-analog conversions on audio signals.
They contain attenuators for volume, squelch, deviation, and compensation. The receiver interface
IC requires a 2.4MHz clock to function (generated by the digital back-end IC) and is programmed by
the microcontroller unit’s SPI bus.
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