Motorola GM660 Service Information - Page 10

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2-4

2.8

Speaker

The controlhead contains a speaker for the receiver audio. The receiver audio signal from the

differential audio output of the audio ampliﬁer located on the radio's controller is fed via connector

J0801-10, 11 to the speaker connector P0801 pin 1 and pin 2. The speaker is connected to the

speaker connector P0801. The controlhead speaker can be disconnected if an external speaker,

connected on the accessory connector, is used.

2.9

Electrostatic Transient Protection

Electrostatic transient protection is provided for the sensitive components in the controlhead by

diodes VR0811 VR00812 VR0816 - VR0817. The diodes limit any transient voltages to tolerable

levels. The associated capacitors provide Radio Frequency Interference (RFI) protection.

3.0

Controlhead Model for GM160, GM360 and GM660

The controlhead contains the internal speaker, the on/off/volume knob, the microphone connector,

several buttons to operate the radio, several indicator Light Emitting Diodes (LED) to inform the user

about the radio status, and a 14 character Liquid Crystal Display (LCD) for alpha - numerical

information e.g. channel number or call address name. To control the LED's and the LCD, and to

communicate with the host radio the controlhead uses the Motorola 68HC11E9 microprocessor.

3.1

Power Supplies

The power supply to the controlhead is taken from the host radio's FLT A+ voltage via connector

J0801 pin 3 and the regulated +5V via connector J0801 pin 7. The voltage FLT A+ is at battery level

and is used for the LED's, the back light and to power up the radio via on / off / volume knob. The

stabilized +5 volt is used for the microprocessor, the display, the display driver and the keypad

buttons. The voltage USW 5V derived from the FLT A+ voltage and stabilized by the series

combination of R0822, VR0822 is used to buffer the internal RAM of the microprocessor (U0831).

C0822 allows the battery voltage to be disconnected for a couple of seconds without losing RAM

parameters. Dual diode D0822 prevents radio circuitry from discharging this capacitor. When the

supply voltage is applied to the radio, C0822 is charged via R0822 and D0822. To avoid that the µP

enters the wrong mode when the radio is switched on while the voltage across C0822 is still too low,

the regulated 5V charge C0822 via diode D0822.

3.2

On / Off

Power

The On/Off/Volume knob when pressed switches the radio's voltage regulators on by connecting line

ON OFF CONTROL to line UNSW 5V via D0821. Additionally, 5 volts at the base of digital transistor

Q0822 informs the controlhead's microprocessor about the pressed knob. The microprocessor

asserts pin 62 and line CH REQUEST low to hold line ON OFF CONTROL at 5 volts via Q0823 and

D0821. The high line ON OFF CONTROL also informs the host radio, that the controlhead's

microprocessor wants to send data via SBEP bus. When the radio returns a data request message,

the microprocessor will inform the radio about the pressed knob. If the radio was switched off, the

radio's µP will switch it on and vice versa. If the On/Off/Volume knob is pressed while the radio is on,

the software detects a low state on line ON OFF SENSE, the radio is alerted via line ON OFF

CONTROL and sends a data request message. The controlhead µP will inform the radio about the

pressed knob and the radio's µP will switch the radio off.

THEORY OF OPERATION