Theory of Operation: Controller 3-23
3.2 Controller
3.2.1 Controller Overview
This section provides a detailed circuit description of the APX 2000/ APX 4000/ APX 4000Li/ 
APX 1000 (900 MHz) controller design. The controller design consists of the following board and 
flexes: 
Printed Circuit Boards
• Main Board 
• Keypad Board
Flexes
• GCAI (Global Core Accessory Interface) (BT Antenna/TX/RX LED)
• Side Controls 
• Backkit (keypad and mainboard)
• Frontkit (audio/speaker/knob/front display)
•Mic
The controller interconnection diagram (Figure 3-17.) shows the various physical components of the 
design, along with how they are all connected. It also shows the key distinguishes between a flex 
connection and a board-to-board connection. A brief description of each of the components is 
provided below. 
Figure 3-17.  Controller Interconnection Diagram
 
 
Keypad 
Board 
GCAI
 
Front display 
Speaker 
and knob
 
Side 
control
 
Main board 
Mic