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GPIO

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Introduction to GPIOs

What is GPIO?

  • GPIO stands for General-Purpose Input/Output.
  • GPIO pins can be dynamically configured as input or output during runtime.
  • A group of GPIO pins is collectively referred to as a port.

LPC2148 Microcontroller GPIO Overview

Key Features:

  • Two 32-bit GPIO ports: PORT0 and PORT1.

PORT0:

  • 32-bit port, but:
    • 28 pins are configurable as general-purpose input/output.
    • P0.31: Can only function as an output pin.
    • P0.24, P0.26, P0.27: Reserved, not available for use.

PORT1:

  • 32-bit port, but:
    • Only 16 pins (P1.16 – P1.31) are available as general-purpose input/output.

Alternate Functions of GPIO Pins

  • Many pins in PORT0 and PORT1 have alternate functions:
    • Example: P0.0 can function as:
      • TXD (Transmit Data) for UART0
      • PWM1 (Pulse Width Modulation)
  • The alternate function is selected using Pin Function Select Registers.

Note on External Resistors

  • PORT0 pins lack built-in pull-up or pull-down resistors.
    • External resistors are required to ensure stable behavior and avoid floating states.

LPC2148 GPIO Ports

graph LR
    A[GPIO Overview] --> B[PORT0: 32-bit]
    A --> C[PORT1: 32-bit]
    B --> D[28 Configurable Pins]
    B --> E[P0.31: Output Only]
    B --> F[P0.24, P0.26, P0.27: Reserved]
    C --> G[16 Configurable Pins: P1.16-P1.31]
    B --> H[Alternate Functions Available]
    C --> H

Registers

Slow GPIO Registers

  • Legacy Compatibility
    • IOXPIN: Read/Write pin values.
    • IOXSET: Set pins HIGH.
    • IOXDIR: Pin direction control.
    • IOXCLR: Set pins LOW.

Example Usage

IO0DIR = 0x000000F0; // Configure P0.4-P0.7 as output and P0.0-P0.3 as input
IO0SET = (1 << 4);   // Set P0.4 HIGH
IO0CLR = (1 << 4);   // Set P0.4 LOW

Fast GPIO Registers

  • Enhanced Performance (3.5x faster access via ARM local bus).
    • FIOXDIR: Configure pin direction.
    • FIOXMASK: Mask pins for fast access.
    • FIOXPIN: Read/Write pin values.
    • FIOXSET: Set pins HIGH.
    • FIOXCLR: Set pins LOW.

Why “Fast GPIO”?

  • Registers relocated to ARM local bus for quicker access, especially noticeable in assembly code.
graph LR
    SlowGPIO[Slow GPIO Registers] --> IOxPIN[IOxPIN: Read/Write]
    SlowGPIO --> IOXSET[IOxSET: Set HIGH]
    SlowGPIO --> IOXDIR[IOxDIR: Pin Direction]
    SlowGPIO --> IOXCLR[IOxCLR: Set LOW]
    FastGPIO[Fast GPIO Registers] --> FIOxDIR[FIOxDIR: Pin Direction]
    FastGPIO --> FIOxMASK[FIOxMASK: Mask Pins]
    FastGPIO --> FIOxPIN[FIOxPIN: Read/Write]
    FastGPIO --> FIOxSET[FIOxSET: Set HIGH]
    FastGPIO --> FIOxCLR[FIOxCLR: Set LOW]

Example: LED Control Using a Button

Objective

Control an LED connected to P0.0 using a button connected to P0.1.

Code Explanation

  1. Setup:
    • Configure P0.0 as output for LED.
    • Configure P0.1 as input for button.
  2. Logic:
    • Turn LED ON if the button is pressed.
    • Turn LED OFF otherwise.

Code Example

#include <lpc214x.h>
#include <stdint.h>
 
int main(void) {
    PINSEL0 = 0x00000000; // Configure P0.0-P0.15 as GPIO
    IO0DIR = 0x00000001;  // P0.0 as output, P0.1 as input
 
    while (1) {
        if (IO0PIN & (1 << 1)) {  // If button (P0.1) is pressed
            IO0SET = 0x00000001;  // Turn LED ON (P0.0 HIGH)
        } else {                  // If button is not pressed
            IO0CLR = 0x00000001;  // Turn LED OFF (P0.0 LOW)
        }
    }
}

LCD 16x2 Interfacing with LPC2148

What is LCD 16x2?

  • A commonly used display module in embedded systems.
  • Features:
    • 16 pins in total:
      • Data Pins (D0-D7): Handle data communication.
      • Control Pins:
        • RS (Register Select): Determines command or data mode.
        • RW (Read/Write): Configures read or write operations.
        • EN (Enable): Signals when data is ready to be read/written.
      • Other pins manage power supply and backlighting.

Modes and Configuration

  • Command Mode:
    • RS = 0, RW = 0: Send configuration commands (e.g., setting display properties).
  • Data Mode:
    • RS = 1, RW = 0: Send actual data to display (e.g., characters).
  • Operating Modes:
    • 4-bit mode: Uses fewer data lines.
    • 8-bit mode: Full data communication.

Example Interfacing LCD with LPC2148

Pin Connections

  • Data Pins (D0-D7): Connected to P0.8-P0.15 of PORT0.
  • Control Pins:
    • RS: Connected to P0.4.
    • RW: Connected to P0.5.
    • EN: Connected to P0.6.

LCD Programming

1. Initialization

  • Configure GPIO pins for LCD data and control.
  • Send initialization commands to the LCD.
void lcd_init(void) {
    IO0DIR = 0x0000FFF0;  // Configure P0.8-P0.15 as data lines, P0.4, P0.5, P0.6 as control lines
    delay_ms(20);         // Wait for LCD to power up
    lcd_command(0x38);    // Initialize in 8-bit mode
    lcd_command(0x0C);    // Display ON, Cursor OFF
    lcd_command(0x06);    // Auto-increment cursor
    lcd_command(0x01);    // Clear display
    lcd_command(0x80);    // Move cursor to first line, first position
}

2. Command Write Function

  • RS = 0, RW = 0: Send configuration commands.
  • Generate enable pulse (high to low).
void lcd_command(char command) {
    IO0PIN = (IO0PIN & 0xFFFF00FF) | (command << 8); // Send command to data pins
    IO0SET = 0x00000040;  // EN = 1
    IO0CLR = 0x00000030;  // RS = 0, RW = 0
    delay_ms(2);          // Wait for command execution
    IO0CLR = 0x00000040;  // EN = 0
    delay_ms(5);
}

3. Data Write Function

  • RS = 1, RW = 0: Send data to display characters.
  • Generate enable pulse (high to low).
void lcd_data(char data) {
    IO0PIN = (IO0PIN & 0xFFFF00FF) | (data << 8); // Send data to data pins
    IO0SET = 0x00000050;  // RS = 1, EN = 1
    IO0CLR = 0x00000020;  // RW = 0
    delay_ms(2);          // Wait for data execution
    IO0CLR = 0x00000040;  // EN = 0
    delay_ms(5);
}

Example Interfacing LCD with LPC2148 in 4-bit Mode

Pin Connections

  • Data Pins (D4-D7): Connected to P0.8-P0.11 of PORT0.
  • Control Pins:
    • RS: Connected to P0.4.
    • RW: Connected to P0.5.
    • EN: Connected to P0.6.

LCD Programming

1. Initialization

  • Configure GPIO pins for LCD data and control.
  • Send initialization commands to set up 4-bit mode.
void lcd_init(void) {
    IO0DIR = 0x00000FF0;  // Configure P0.8-P0.11 as data lines, P0.4, P0.5, P0.6 as control lines
    delay_ms(20);         // Wait for LCD to power up
    lcd_command(0x02);    // Initialize in 4-bit mode
    lcd_command(0x28);    // 2-line, 4-bit mode, 5x7 font
    lcd_command(0x0C);    // Display ON, Cursor OFF
    lcd_command(0x06);    // Auto-increment cursor
    lcd_command(0x01);    // Clear display
    lcd_command(0x80);    // Move cursor to first line, first position
}

2. Command Write Function

  • RS = 0, RW = 0: Send configuration commands.
  • Send higher nibble first, then lower nibble.
  • Generate enable pulse (high to low).
void lcd_command(char command) {
    IO0PIN = (IO0PIN & 0xFFFFF0FF) | ((command & 0xF0) << 4); // Send higher nibble
    IO0CLR = 0x00000030;  // RS = 0, RW = 0
    IO0SET = 0x00000040;  // EN = 1
    delay_ms(2);
    IO0CLR = 0x00000040;  // EN = 0
    
    IO0PIN = (IO0PIN & 0xFFFFF0FF) | ((command & 0x0F) << 8); // Send lower nibble
    IO0SET = 0x00000040;  // EN = 1
    delay_ms(2);
    IO0CLR = 0x00000040;  // EN = 0
    delay_ms(5);          // Wait for command execution
}

3. Data Write Function

  • RS = 1, RW = 0: Send data to display characters.
  • Send higher nibble first, then lower nibble.
  • Generate enable pulse (high to low).
void lcd_data(char data) {
    IO0PIN = (IO0PIN & 0xFFFFF0FF) | ((data & 0xF0) << 4); // Send higher nibble
    IO0SET = 0x00000050;  // RS = 1, EN = 1
    IO0CLR = 0x00000020;  // RW = 0
    delay_ms(2);
    IO0CLR = 0x00000040;  // EN = 0
    
    IO0PIN = (IO0PIN & 0xFFFFF0FF) | ((data & 0x0F) << 8); // Send lower nibble
    IO0SET = 0x00000050;  // RS = 1, EN = 1
    IO0CLR = 0x00000020;  // RW = 0
    delay_ms(2);
    IO0CLR = 0x00000040;  // EN = 0
    delay_ms(5);          // Wait for data execution
}

Graph View

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