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The SLIC acts as an extension of the microcontrol unit by providing
logic functions such as lower address latch, reset, memory address
decoding, and additional control lines for the radio. The microcontrol
unit controls the crystal-pull circuit to adjust the crystal oscillator’s
frequency on the microcontrol unit, so that the E-clock’ s harmonics
do not cause interference with the radio’s receive channel.
Switched +5V is used for all circuits on the VOCON board except the
audio PA, which is sourced from 7.5V. The regulator automatically
provides 5V when the radio is turned on. The regulator’s power-down
mode is controlled by the microcontrol unit, which senses the
position of the on/off/volume control knob.
The DSP performs all signalling and voice encoding and decoding as
well as audio filtering and volume control. This includes Private-
Line®/Digital Private Line™ (PL/DPL) encode and alert-tone
generation. The IC transmits pre-emphasis on analog signals and
applies a low-pass (splatter) filter to all transmitted signals. It is
programmed using parallel programming from the microcontrol unit
and the ADSIC.
The ADSIC performs analog-to-digital and digital-to-analog
conversions on audio signals. It contains attenuators for volume,
squelch, deviation, and compensation, and it executes receiver
filtering and discrimination. The IC requires a 2.4MHz clock to
function (generated by the ABACUS IC) and is programmed by the
microcontrol unit SPI bus.
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General
