3-4 Keypad: Controller Board
3.1.5 Audio/Signaling
The audio/signalling/filter/companding IC (ASFIC) and the audio power amplifier (Figure 3-2 on
page 3-2) form the main components of the audio/signalling section of the controller board. Inputs
include a 16.8 MHz clock from the synthesizer, recovered audio and squelch, MCU control signals,
and external or internal microphones. Outputs include a microprocessor clock (CLK), modulator
output to the synthesizer, and amplified audio signals to an internal or external speaker.