Mechanical On/Off; Ignition; Microprocessor Clock Synthesizer - Motorola GM328 Service Manual

Controller Circuits
1.6

Mechanical ON/OFF

This refers to the typical On/Off/Volume knob, located on the controlhead, and which turns the radio
on and off.
If the radio is turned off and the On/Off/Volume knob is pressed, line ON OFF CONTROL (J0401 pin
11) goes high and switches the radio's voltage regulators on as long as the button is pressed. The
microprocessor is alerted through line ON OFF SENSE (U0101 pin 6) which is pulled to low by
Q0110 while the On/Off /Volume knob is pressed. In addition, an interrupt is generated at µP pin 96.
The µP asserts line DC POWER ON via ASFIC CMP, pin 13 high which keeps Q0661 and Q0641,
and in turn the radio, switched on. When the On/Off/Volume knob is released again the controlhead
informs the µP via SBEP bus about the knob release. (See SBEP Serial Interface subsection for
more details). This informs the µP to keep the radio switched on and continue with normal operation.
If the On/Off/Volume knob is pressed while the radio is on, the controlhead informs the µP via SBEP
bus about the knob status. (See SBEP Serial Interface subsection for more details). After a short
delay time the microprocessor switches the radio off by setting DC POWER ON to low via ASFIC
CMP pin 13.
1.7

Ignition

Ignition sense is used to prevent the radio from draining the vehicle's battery because the engine is
not running.
When the IGNITION input (J0501 pin 10) goes above 5 volts Q0661 is turned on via line IGNITION
CONTROL. Q0661 turns on INT SW B+ and the voltage regulators by turning on Q0641 and the
microprocessor starts execution. The microprocessor is alerted through line GP6 IN ACC10. The
voltage at the IGNITION input turns Q0181 on, which pulls microprocessor pin 74 to low. If the
software detects a low state it asserts DC POWER ON via ASFIC pin 13 high which keeps Q0661
and Q0641, and in turn the radio switched on.
When the IGNITION input goes below 3 volts, Q0181 switches off and R0181 pulls microprocessor
pin 74 to high. This alerts the software to switch off the radio by setting DC POWER ON to low. The
next time the IGNITION input goes above 5 volts the above process will be repeated.
1.8

Microprocessor Clock Synthesizer

The clock source for the microprocessor system is generated by the ASFIC CMP (U0221). Upon
power-up the synthesizer IC (FRAC-N) generates a 16.8 MHz waveform that is routed from the RF
section to the ASFIC CMP pin 34. For the main board controller the ASFIC CMP uses 16.8 MHz as
a reference input clock signal for its internal synthesizer. The ASFIC CMP, in addition to audio
circuitry, has a programmable synthesizer which can generate a synthesized signal ranging from
1200Hz to 32.769MHz in 1200Hz steps.
When power is first applied, the ASFIC CMP will generate its default 3.6864MHz CMOS square
wave UP CLK (on U0221 pin 28) and this is routed to the microprocessor (U0101 pin 90). After the
microprocessor starts operation, it reprograms the ASFIC CMP clock synthesizer to a higher UP
CLK frequency (usually 7.3728 or 14.7456 MHz) and continues operation.
The ASFIC CMP may be reprogrammed to change the clock synthesizer frequencies at various
times depending on the software features that are executing. In addition, the clock frequency of the
synthesizer is changed in small amounts if there is a possibility of harmonics of this clock source
interfering with the desired radio receive frequency.
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