Motorola Gm Series Detailed 6864115b62 B Manual

Chapter 2
THEORY OF OPERATION
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 Section of this manual.
2.0 Controlhead Model for GM140, GM340 and GM640
The controlhead contains the internal speaker, the on/off/volume knob, the microphone connector, 
several buttons to operate the radio and several indicator Light Emitting Diodes (LED) to inform the 
user about the radio status. To control the...

2-2THEORY OF OPERATION
The microprocessor’s RAM is always powered to maintain parameters such as the last operating 
mode. This is achieved by maintaining 5V at µP  pin 25. Under normal conditions, when the radio is 
off, USW 5V is formed by FLT A+ running to D0822. C0822 allows the battery voltage to be 
disconnected for a couple of seconds without losing RAM parameters. Diode D0822 prevents radio 
circuitry from discharging this capacitor.
There are 8 analogue to digital converter ports (A/D) on the µP...

Controlhead Model for GM140, GM340 and GM640 2-3
An additional pair of analogue lines and A/D µP  ports (PE 3 – 2) is available to support a keypad 
microphone, connected to the microphone connector J0811. Any microphone key press is processed 
the same way as a key press on the controlhead.
2.6 Status LED and Back Light Circuit
All indicator LED’s (red, yellow, green) are driven by current sources. To change the LED status the 
host radio sends a data message via SBEP bus to the controlhead µP . The...

2-4THEORY OF OPERATION
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...

Controlhead Model for GM160, GM360 and GM660 2-5
3.3 Microprocessor Circuit
The controlhead uses the Motorola 68HC11E9 microprocessor (µP) (U0831) to control the LED’s 
and the LCD and to communicate with the host radio. RAM and ROM are contained within the 
microprocessor itself.
The microprocessor generates it’s clock using the oscillator inside the microprocessor along with a 8 
MHz ceramic resonator (U0833) and R0920 .
The microprocessor’s RAM is always powered to maintain parameters such as the last...

2-6THEORY OF OPERATION
3.5 Keypad Keys
The controlhead keypad is a 6-key kepad (Model B) or a 10- key keypad (model C). All keys are 
configured as 2 analogue lines read by µP  pins 13 and 15. The voltage on the analogue lines varies 
between 0 volts and +5 volts depending on which key has been pressed. If no key is pressed, the 
voltage at both lines will be 5 volts. The key configuration can be thought of as a matrix, where the 
two lines represent one row and one column. Each line is connected to a...

Controlhead Model for GM160, GM360 and GM660 2-7
includes the RAM start address for the following display data. With input A0 set to logic „1 the µP  
then writes the display data to the display RAM. When data transfer is complete the µP terminates 
the chip select, RD and WD activities.
The display driver’s power circuit provides the voltage supply for the display. This circuit consists of a 
voltage multiplier, voltage regulator and a voltage follower. The external capacitors C0971 - C0973 
configure...

2-8THEORY OF OPERATION
3.9 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.
3.10 Electrostatic Transient...

Controlhead Model for GM380, and GM12802-9
prevents radio circuitry from discharging this capacitor. The +5V at the second anode of D0855 
speeds up charging of C0856, when the host radio is turned on by a high level at the ignition input 
while the supply voltage is applied to the radio. This prevents the microprocessor from accidently 
entering bootstrap mode.
4.3 Power On / Off
The On/Off/Volume knob when pressed switches the radio’s and the controlhead‘s voltage regulators 
on by connecting line ON...

2-10THEORY OF OPERATION
controlhead µP can drive the line. The microprocessor sends serial data via pin 79 and D0872 and it 
reads serial data via pin 78. Whenever the microprocessor detects activity on the BUS+ line, it starts 
communication.
When the host radio needs to communicate to the controlhead µP, it sends data via line BUS+. Any 
transition on this line generates an interrupt and the µP starts communication. The host radio may 
send data like display information, LED and back light status or it...