Microcontroller - Motorola CP185 Basic Service Manual

2-8
The TX audio enters the radio via the internal MIC or external MIC. This TX Audio is filtered through
a 4th order 4 kHz Low-pass filter (U501-C & D) which prevents aliasing noise from ASIC. TX Audio
enters the Audio Processor IC which is then directed to an internal Amplifier (TX A1) for gain
adjustment of audio signal. A HPF (VR1) controls the input level of TX audio signal from -6.0 dB to
+4.5 dB in 1.5 dB steps. A Compressor (if ON) compresses the amplitude of TX audio signal by
0.5 dB. A Pre-emphasis circuit (if ON) emphasizes the high frequency component of TX audio signal
to improve Signal to Noise ratio before modulation. A shared High-pass filter (TX/RX HPF)
eliminates low-frequency components <250 Hz from TX audio signal. A Limiter is used to limit the
signal amplitude and suppress frequency deviation during modulation. VR2 controls the output level
from -9.6 dB to +3.0 dB in 0.2 dB steps. A Splatter (LPF) eliminates high-frequency components
>3 kHz. A Smoothing filter (SMF) eliminates high-frequency and clock components generated
internally by ASIC.
For sub-tone data from CPU, DTA1 amplifies the signal, sends it through a Sub-audio Programmable
LPF to eliminate components of DAT1 amplification, and finally the signal is regulated by VR5 from
-6.0 dB to +6.0 dB in 0.5 dB steps. The final sub-tone data passes through a 2nd order LPF
(U502-A) before it is mixed with TX Audio for modulation.
UHF1 and UHF2 : The processed TX audio signal from Audio Processor IC is amplified by TX audio
frequency amplifier (U502-C) to increase limiting range and then adjusted to a proper level for
modulation by U508.
VHF: The processed TX audio signal from Audio Processor IC is adjusted to proper level for
modulation by U508 before amplified by TX audio frequency amplifier (U502-C) to increase limiting
range.
Final TX Audio signal passes through a 6th order 3 kHz low pass filter (U501-A & B) before sent to
VCO for modulation.
Note: Retune the TX modulation if U508 is replaced. Refer
Options on page 5-4.
The output audio signal of Audio Processor IC is directed to volume control switch (SW/VOL1)
controlled by user and is finally amplified by U601BTL Audio Amplifier to a sufficient level to drive
either the external or internal speaker.
2.2.6

Microcontroller

The microprocessor or CPU includes Microprocessor (U101), EEPROM and support components.
Radio operation is controlled by software in internal Flash ROM memory.
Radio parameters and customer specific information is stored in External EEPROM (U104). Pins 35
and 36 controls the Sub-PCB mounted LED indicators. PTT button (PB501) is linked to CPU via pin
44. Side programmable buttons 1 and 2 (PB502 and PB503) is linked via pin 21 and 32, respectively.
Customer Programming Software (CPS) connects to the radio via a USB Programming cable
(PMDN4077_R) through the microphone port (J601 pin 6) to pin 34 and 33 (PRG/CLONE_RX and
PRG/CLONE_TX port). A 7.3728 MHz clock signal (X-in) is provided by FL101 to CPU. A voltage
divider system (R153 and R154) is used by CPU to sense battery level.
Theory Of Operation: Major Assemblies
Chapter 5.5: Transmitter Alignment