Cpu And Peripheral Circuits - Alinco DJ-493 Service Manual

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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 (DJ-496)
The PLL (IC2) uses the reference frequency, 5 or 6.25kHz. The phase com­
parator in the IC2 compares the phase of the frequency from the VCO with
that of the comparison frequency, 5 or 6.25kHz, which is obtained by the inter­
nal divider in IC2.
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 IC2
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 Q3 directly oscillates the desired fre­
quency. The frequency control voltage determined in the CPU (IC9) and PLL
circuit is input to the varicaps (D3). This change the oscillation frequency, 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 1/4 the bias, at the frame frequency is 112.5Hz.
When the LAMP key is pressed, "H" is output form pin 42 of CPU (IC9) to the
bases of Q19, Q24 and Q25.
When the power form the DC jack or external battery increases from Circuits 0
V to 2.5V or more, "H" level reset signal is output from 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 until the CPU clock (X3) has stabi­
lized.
The DC potential of pin 8 of iC4 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 R179 and R180 (for level adjust-ment), and then
through the microphone amplifier (IC8), 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.