Hytera MD78X, Service Manual

Page: 134 / 519

UHF2 (450
–
520 MHz)
Circuit Description
21
Pin
No.
Signal Function
I/O of
the
Radio
Voltage
(Option Board
VDD=3.3 V)
Remarks
18 AF MB TO OB AF O
80 mV (standard
output from the main
board to the option
board)
MAX: 700mV
19 DGND DGND / / /
20 3V6 or 5V Power O Voltage: 5.0 V /
5.2.3
Audio Module
The audio module is used to output RX audio and input relay audio and TX audio, which serves as the
RX audio path and TX audio path.

RX Audio Path
U302 sends digital audio signals to the audio processor codec (U231) via the SSI bus of
MCBSP1.This bus is composed of CLKX, FSX, DX and DR. It sends the 16-digit demodulated PCM
audio signal to the codec (U231), and adjusts the signal to appropriate amplitude according to the