User manual

Installation and Operation

2.4 GPIO EXPANDER KEYPAD AND LCD DEMO BOARD DESCRIPTION

2.4.1 Major Board Components

The functional block diagram is shown in Figure 2-2.

FIGURE 2-2: FUNCTIONAL BLOCK DIAGRAM

1. The GPIO BLOCK contains the MCP23X17 and MCP23X08 GPIO Expanders.

Two (2) MCP23X17 devices are connected to the LCD module and two (2)

MCP23X08 devices are connected to the keypad matrix.

A button on the keypad toggles between I

C and SPI mode. When in I

C mode,

the MCP23017 and MCP23008 are controlled by the PIC MCU. When in SPI

mode, the MCP23S17 and MCP23S08 are controlled. Only one (1) MCP23X08

and one (1) MCP23X17 is on the bus at a time.

2. The CONTROL BLOCK contains the PIC18F4550 and is the main intelligence

in the system.

3. The INPUT BLOCK contains the 4x4 keypad matrix. The MCP23X08 devices

are used to scan the keys.

4. The OUTPUT BLOCK contains the 2x16 LCD. The MCP23X17 devices control

the display.

5. The MCP23X17 and MCP23X08 I/O and serial lines are routed to the HEADER

BLOCK to allow the pins to be probed.

6. The PROGRAMMING BLOCK contains the ICSP™ header for program-

ming/debugging the PIC18F4550.

7. The POWER BLOCK contains the MCP1702 5V voltage regulator. The board

can be powered by a 9V supply (connected through the power jack) or by

applying 5V directly to the power points.

Control

Power

GPIO

Header

OUTIN

Programming

2 X 16 LCD

Input Output