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1.0

Introduction

This Chapter provides a detailed theory of operation for the Controlhead circuits. For details of the

trouble shooting refer to the related chapter in this section.

2.0

Controlhead Model for CM140 and CM340

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

several buttons to operate the radio and three indicator Light Emitting Diodes (LED) to inform the

user about the radio status and a 7-segment display for numeric information.

7-segment

display

DTMF

Resistors

Keypads

2.1

Power Supplies

The power supply to the control head is taken from the host radio's 9.3V via connector J803-9, The

9.3V is used for the LEDs and back light, the 5V is used for the LCD driver and level shifter. The

stabilized 3V is used for the other parts.

2.2

SPI Interface

The host radio (master) communicates with the control head through its SPI bus. Three lines are

connected to the shift register (U801):SPI clock (J803-17), SPI MOSI (J803-16) and shift register

chip select (J803-15).

BCD To

7-segment

Control line

Boot_res / SCI

Mux.

Control

DTMF

Row/Column

9.3V

Keypad

Backlight

THEORY OF OPERATION

9.3V

Shift

PTT

circuit

Boot_res (DTMF-

Column)/ SCI

(DTMF-Row)

Chapter 2

2 pin speaker

connector