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4.3 - 8
Motorcycle Control Head
The Control Head forms the interface between the radio and the user. It includes an LCD display, an
ON/OFF switch/volume control, and keypad and control keys.
The microprocessor-controlled Control Head interfaces with the radio control logic board's J650
(Model A), or J4 (Model B) via an 18-pin connector on the back of the unit. A handset or external
microphone are connected to the Control Head via the front-mounted microphone connector, J2.
Power Supplies
Power supply A+ (pin 17) is routed directly from the radio battery and is used for LCD and keypad
backlight LEDs and indicator LEDs.
Power supply SW_B+ (pin 18) is routed from the radio battery via the radio ON/OFF switch; it pro-
vides Vcc via regulator U9. It is also routed to J2 for handset power supply.
Volume Control / ON/OFF Switch
Front panel switch/potentiometer U5 controls the volume via A/D convertor PD0 (pin 14) in micro-
controller (µC) U4. The centre of the potentiometer is a push button switch used for microphone
input and power ON/OFF. When activated, the microphone line (pin 9) is connected to ground.
Microcontroller (U4)
Microcontroller U4 and data expander U6 control the operation of the Control Head. The µC
exchanges data with the radio via the SB9600 bus (TD0 and RD1). In addition, keypad and LCD
data is processed via ports A, B, and C. Both the µC and the expander are reset by undervoltage
detector U7 when Vcc drops below 4.65 volts. Both devices can also be reset from the radio via the
reset line (pin 3) and Q14.
Crystal Oscillator
The crystal oscillator is built using on-chip oscillator gates on the microprocessor. The crystal is a
standard 4 MHz ceramic resonator.
LCD Display
The display (U1) is a double-layer, super-twist LCD display. It has two lines of 14 characters, and
one line of 20 fixed symbols at the top of the display.
Backlight
The backlight consists of 48 LEDs. Light intensity is in four levels, including off, and is software-con-
trolled by bus commands via expander U6 (Q2, Q15). A high-temperature condition in the Control
Head overrides the software commands; if the temperature rises to 78ºC or above, the lowest light
level, or off, will be selected.
MTM700 Mobile Radio / Detailed Service Manual
THEORY OF OPERATION (CONTROL HEADS)
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