Uniden SMH 4000, Руководство по обслуживанию

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The operating speed of the microproces­
sor is determined by the crystal (X601)
connected between pins 29 and 30 of
IC601. The Xin port (IC601, pin 29) is the
input to the internal oscillator, and the Xout
port (IC601, pin 30) is the output of the os­
cillator which also provides the feedback to
maintain oscillation. The oscillator frequen­
cy is divided into signals that become the
microprocessor timing signals. A timing sig­
nal is output when serial data transfer
takes place, for use as external
synchronous timing.
The microprocessor has 57
1/0
lines for
use as input/output lines for data and con­
trol. These lines are broken up into six 8-
bit and one 4-bit data ports and five control
ports.
When the microprocessor sends data to
the PLL, it is sent as synchronous serial
data from IC601, pin 1 O with clock pulses
sent from IC601, pin 9. The PLL (IC403)
receives reference counter data (16 bits of
data followed by pulsing the enable line
high, IC601, pin 57), followed by the "N"
and "A" counter data (20 bits of data fol­
lowed by pulsing the enable line high.)
When the microprocessor sends data to
the DISPLAY LED it is sent as
synchronous serial data from IC601, pin
54 with clock pulses sent from IC601, pin
52. While data is being sent to the DIS­
PLAY LED the IC601, pin 53 is held low,
thus preventing the LEDs from flashing
with the data stream. Each time the chan­
nel is changed, or the PushToTalk button
is pressed, the microprocessor reads data
from the E2PROM, and sends data to the
PLL and LEDs.
The microprocessor is reset each time that
power is applied to the unit, or when the
voltage drops below the operating voltage
of the microprocessor. When the operating
voltage falls below 5 volts, 0608 starts con­
ducting, thereby pulling the reset line low.
As the voltage increases to the 5-volt level,
0608 stops conducting, pulling the reset
line high, thus resetting the
microprocessor.
December 1 992
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