P3.0 is the serial programmer receive data line. P3.1 is the serial programmer transmit data
line.
P3.2 is the low volts interrupt input. When the supply voltage to the mobile drops below 9.8
volts this pin will go to a logic low level.
P3.3 is the analogue signalling interrupt input pin. This pin will have a series of pulses approx
20uSec wide appearing on it.
P3.4 controls the alert tone generator. A logic low from this output will turn on the alert tone
generator.
Lines P3.5, P3.6 and P3.7 are used to set each column low in turn so that the pressed key
may be read by ports P0.0, P0. 1 and P0.2.
3.2.4.6 SERIAL LATCH
The serial latch IC207, controls the following radio functions.
Q0 Transmit power control
Q 1 Receiver mute control
Q2 External alarm output
Q3 Transmit PA enable
Q4 Transmitter enable
Q5 Microphone mute control
Q6 Crystal oscillator shift control
Q7 Synthesizer switch control
Q0 is the transmit power control line. A logic 0 level on this line indicates high transmitter
power. A logic 1 level sets the transmitter for low power.
Q1 is the receiver mute control. A logic 1 on this line mutes the received audio.
Q2 is the external alarm output. This output controls an open collector transistor.
Q3 is the transmitter power amplifier enable. A high level on this pin will enable the
transmitter.
Q4 is the transmitter enable line. When this line is at a logic high level the 9-volt power to the
receiver is disabled and the 9-volt power to the transmitter is enabled.
Q5 is the microphone mute line. A logic 1 level on this line mutes the transmit audio.
Q6 is the crystal oscillator shift line. When this line is high the frequency of the crystal
oscillator is moved in frequency by -500ppm.
Q7 is the synthesizer switch line. This line is used to lower the noise output of the synthesizer
control loop.
Section 3 Page 23
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