Cpu And Peripheral Circuits - Alinco DJ-195 Service Manual

3. Phase Comparator Circuit
4. PLL Loop Filter Circuit
5. VCO Circuit

4) CPU and Peripheral Circuits

1. LCD Display Circuit
2. Display Lamp Circuit
3. Reset and Backup
4. S(Signal) Meter Circuit
5. DTMF Encoder
The PLL (IC1) uses the reference frequency, 5 or 6.25kHz. The phase com-
parator in the IC1 compares the phase of the frequency from the VCO with that
of the comparison frequency, 5 or 6.25kHz, which is obtained by the internal
divider in IC1.
If a phase difference is found in the phase comparison between the reference
frequency and VCO output frequency, the charge pump output (pin 8) of IC1
generates a pulse signal, which is converted to DC voltage by the PLL loop
filter and input to the varicap of the VCO unit for oscillation frequency control.
A Colpitts oscillation circuit driven by Q1 directly oscillates the desired fre-
quency. The frequency control voltage determined in the CPU (IC9) and PLL
circuit is input to the varicaps (D32 and D34). This change the oscillation fre-
quency, which is amplified by the VCO buffer (Q5) and output from the VCO
unit.
The CPU turns ON the LCD via segment and common terminals with 1/4 the
duty and 1/3 the bias, at the frame frequency is 112.5Hz.
When the LAMP key is pressed, "H" is output form pin 50 of CPU (IC9) to the
bases of Q12. Q12 then turn ON and the LEDs (D12 and D17) light.
When the power form the DC jack or external battery increases from Circuits 0
V to 2.5 or more, "H" level reset signal is output form the reset IC (IC11) to pin
33 of the CPU (IC9), causing the CPU to reset. The reset signal, however,
waits at 100, and does not enter the CPU untilthe CPU clock (X2) has stabi-
lized.
The DC potential of pin 8 of IC5 is input to pin 1 of the CPU (IC9), converted
from an analog to a digital signal, and displayed as the S-meter signal on the
LCD.
The CPU (IC9) is equipped with an internal DTMF encoder. The DTMF signal
is output from pin 10, through R102 and R158 (for level adjust-ment), and then
through the microphone amplifier (IC7), and is sent to the varicap of the VCO
for modulation. At the same time, the monitor-ing tone passes through the AF
circuit and is output form the speaker.6. CTCSS Encoder The CPU (IC9) is
equipped with an internal tone encoder. The tone signal (67.0 to 250.3 Hz) is
output form pin 9 of the CPU to the varicap (D3) of the VCO for modulation.
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