Electronic On/Off; Emergency - Motorola GM328 Service Manual

1-4
1.4

Electronic ON/OFF

The radio has circuitry which allows radio software and/or external triggers to turn the radio on or off
without direct user action. For example, automatic turn on when ignition is sensed and off when
ignition is off.
Q0661 is used to provide INT SW B+ to the various radio circuits and to enable the voltage
regulators via transistor Q0641. Q0661 contains an pnp and an npn transistor and acts as an
electronic on/off switch. The switch is on when the collector of the npn transistor within Q0661 is low.
When the radio is off the collector is at supply voltage level. This effectively prevents current flow
from emitter to collector of the pnp transistor. When the radio is turned on the voltage at the base of
the npn transistor is pulled high and the pnp transistor switches on (saturation). With voltage INT
SWB+ now at supply voltage level, transistor Q0641 pulls pin 2 of the voltage regulators U0611 and
U 0641 to ground level and thereby enables their outputs.
The electronic on/off circuitry can be enabled by the microprocessor (through ASFIC CMP port
GCB2, line DC POWER ON), the emergency switch (line EMERGENCY CONTROL), the
mechanical On/Off/Volume knob on the controlhead (line ON OFF CONTROL), or the ignition sense
circuitry (line IGNITION CONTROL). If any of the 4 paths cause a low at the collector of the npn
transistor within Q0661, the electronic "ON" is engaged.
1.5

Emergency

The emergency switch (J0501 pin 9), when engaged, grounds the base of Q0662 via line
EMERGENCY CONTROL. This switches Q0662 off and resistor R0662 pulls the collector of Q0662
and the base of Q0663 to levels above 2 volts. Transistor Q0663 switches on and pulls the collector
of the npn transistor within Q0661 to ground level and thereby enables the voltage regulators via
Q0641. When the emergency switch is released R0541 pulls the base of Q0662 up to 0.6 volts. This
causes the collector of transistor Q0662 to go low (0.2V), thereby switching Q0663 off.
While the radio is switched on, the microprocessor monitors the voltage at the emergency input on
the accessory connector via pin 60 and line GP5 IN ACC9. Three different conditions are
distinguished, no emergency, emergency, and open connection to the emergency switch. If no
emergency switch is connected or the connection to the emergency switch is broken, the resistive
divider R0541 / R0512 will set the voltage to about 4.7 volts. If an emergency switch is connected, a
resistor to ground within the emergency switch will reduce the voltage on line GP5 IN ACC9 to
inform the microprocessor that the emergency switch is operational. An engaged emergency switch
pulls line GP5 IN ACC9 to ground level. Diode D0179 limits the voltage to protect the
microprocessor input.
While EMERGENCY CONTROL is low, INT SW B+ is on, the microprocessor starts execution,
reads that the emergency input is active through the voltage level of line GP5 IN ACC9, and sets the
DC POWER ON output of the ASFIC CMP pin 13 to a logic high. This high will keep Q0661 and
Q0641 switched on. This operation allows a momentary press of the emergency switch to power up
the radio. When the microprocessor has finished processing the emergency press, it sets the DC
POWER ON line to a logic 0. This turns off Q0661 and the radio turns off. Notice that the
microprocessor is alerted to the emergency condition via line GP5 IN ACC9. If the radio was already
on when emergency was triggered then DC POWER ON would already be high.
Controller Circuits