Motorola Gm Series Detailed 6864115b62 B Manual

Controller Circuits1-3
The voltage VSTBY, which is derived  directly from the supply voltage by components R0621 and 
VR0621, is used to buffer the internal RAM. C0622 allows the battery voltage to be disconnected for 
a couple of seconds without losing RAM parameters. Dual diode D0621 prevents radio circuitry from 
discharging this capacitor.  When the supply voltage is applied to the radio, C0622 is charged via 
R0621 and D0621. To avoid that the µP enters the wrong mode when the radio is switched on...

1-4THEORY OF OPERATION
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),...

Controller Circuits1-5
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...

1-6THEORY OF OPERATION
On the controller there are two ICs on the SPI BUS, ASFIC CMP (U0221-22), and EEPROM 
(U0111-5). In the RF sections there are 2 ICs on the SPI BUS, the FRAC-N Synthesizer, and the 
Power Control IC (PCIC). The SPI TRANSMIT DATA and CLK lines going to the RF section are 
filtered by L0481 / R0481 and L0482 / R0482 to minimize noise. The chip select line CSX from 
U0101 pin 2 is shared by the ASFIC CMP, FRAC-N Synthesizer and PCIC. Each of these IC‘s check 
the SPI data and when the...

Controller Circuits1-7
DIG OUT 2 can be used as normal output or external alarm output, set by the CPS. Transistor Q0173 
is controlled by the µP via ASFIC CMP pin 14.
DIG IN 3 is read by µP pin 61 via resistor R0176
DIG IN 5 can be used as normal input or emergency input, set by the CPS. The µP reads this port via 
R0179 and µP pin 60. Diode D0179 limits the voltage to protect the µP input.
DIG IN 6 can be used as normal input, set by the CPS. The µP reads this port via pin 74 and Q0181.
DIG IN OUT...

1-8THEORY OF OPERATION
On the µP the lines XIRQ (U0101-48), MODA LIR (U0101-58), MODB VSTPY (U0101-57) and 
RESET (U0101-94) should be high at all times during normal operation. Whenever a data or address 
line becomes open or shorted to an adjacent line, a common symptom is that the RESET line goes 
low periodically, with the period being in the order of 20msecs. In the case of shorted lines you may 
also detect the line periodically at an intermediate level, i.e. around 2.5V when 2 shorted lines...

Controller Board Audio and Signalling Circuits 1-9
1.14 Electrically Erasable Programmable Memory (EEPROM)
The external 16 Kbyte EEPROM (U0111) contains additional radio operating parameters such as 
operating frequency and signalling features, commonly know as the codeplug. It is also used to store 
radio operating state parameters such as current mode and volume. This memory can be written to 
in excess of 100,000 times and will retain the data when power is removed from the radio. The 
memory access...

1-10THEORY OF OPERATION
2.2 Transmit Audio Circuits
Refer to Figure 3-1 for reference for the following sections.
Figure 3-1 Transmit Audio Paths
2.2.1 Mic/Data Input Path
The radio supports 2 distinct microphone paths known as internal (from controlhead) and external 
mic (from accessory connector J0501-2) and an auxiliary path (FLAT TX AUDIO, from accessory 
connector J0501-5). The microphones used for the radio require a DC biasing voltage provided by a 
resistive network.
These two microphone audio...

Controller Board Audio and Signalling Circuits 1-11
C0254 serves as a DC blocking capacitor. Multi switch U0251 controlled by ASFIC CMP port GCB4 
selects either the external microphone input signal or the voice storage playback signal for entering 
the ASFIC CMP at pin 48. The audio signal at U0221-48 (TP0222) should be approximately 14mV 
for 1.5kHz or 3kHz of deviation with 12.5kHz or 25kHz channel spacing.
The FLAT TX AUDIO path is used for transmitting data signals and has therefore no limiter or...

1-12THEORY OF OPERATION
Secure board contains circuitry to amplify, encrypt, and filter the audio. The encrypted signal is then 
fed back from J0551-32 to the ASFIC CMP TX RTN input (U0221-36). The signal level at this pin 
should be about 65mVrms. The signal is then routed through the TX path in the ASFIC CMP and 
emerges at MOD IN pin 40.
2.2.4 Option Board Transmit Audio
The audio follows the normal transmit audio processing until it emerges from the ASFIC CMP TX 
SND pin (U0221-44), which is fed to...