Connecting a Switch to ARM7 LPC2148 Using Embedded C

The ARM7 LPC2148 microcontroller is a powerful device for a variety of embedded systems applications. One common task is interfacing a switch to the microcontroller using GPIO (General Purpose Input Output) pins to control LEDs or perform other necessary functions in embedded systems. This article will guide you through the essential steps of interfacing a switch with an ARM7 LPC2148 using embedded C programming.

Key Components and Setup

ARM7 LPC2148 is a microcontroller designed for embedded systems, with robust GPIO capabilities. To interface a switch effectively, we need to configure the GPIO pins for both input and output purposes.

Configuring GPIO Pins

The GPIO pins on the LPC2148 need to be configured as inputs or outputs. For simplicity and example purposes, we will configure some of the GPIO pins as both inputs and outputs, while others will remain as outputs.

#include "lpc2148.h"
#define LED 16
#define Switch 24
void Delay(int n);
int main(void)
{
  unsigned char Status  1;
  // Configure P1.16 - P1.31 as GPIO
  PINSEL2  FFFFFF3F;
  // Configure P1.24 - P1.31 as Input (LEDs)
  IO1DIR  00;
  // Configure P1.16 - P1.23 as Output (Switch Input)
  IO1DIR  FF;
  while(1)
  {
    Status  1;
    // Set LEDs to HIGH
    IOSET1  FF;
    Delay(10);
    // Set LEDs to LOW
    IOCLR1  FF;
    Delay(10);
    Delay(10);
    Delay(10);
    // Debounce the switch
    while(~Status)
    {
      Status  IO1PIN  FF00FFFF;
      IO1PIN  Status;
    }
  }
}
void Delay(int n)
{
  int p, q;
  for(p  0; p 

Software Setup and Implementation

The C code above demonstrates how to configure the GPIO pins, set up the switch, and implement a simple debounce mechanism to ensure stable switch readings. Below are the detailed steps:

Configuring GPIO Pins: The configuration of GPIO pins is done in the PINSEL2 register. In this example, P1.16 - P1.31 are configured as GPIO, and P1.24 - P1.31 are configured as inputs for controlling LEDs. P1.16 - P1.23 are configured as outputs to read the switch state.

Setting GPIO Direction: We set the IO1DIR register to configure the direction of the pins. IO1DIR 00; sets the LEDs' direction as input, while IO1DIR FF; sets the switch input as output.

Initial Debounce State: We initialize the Status variable to 1, which indicates that the switch is off.

Debouncing the Switch: We continuously read the value of the switch pin and use a simple debounce mechanism. The debounce mechanism checks the state of the switch over a period of milliseconds, ensuring stable readings are taken before proceeding.

LED Control Based on Switch State: The program toggles the LED state based on the status of the switch. This is demonstrated in the loop where the LED is set to high, then low, based on the current switch state.

Compiling and Running the Code

To compile the code above, you will need the KEIL development environment. The code must be added to a project prepared with the correct settings. Once compiled, the generated HEX file should be uploaded to the LPC2148 microcontroller via the development board's UART0.

Flash Magic is a useful tool for flashing the HEX file to the microcontroller. This tool allows you to verify that the program is correctly executed without any hardware setup.

Conclusion

Interfacing a switch to an ARM7 LPC2148 using embedded C is a fundamental task in microcontroller programming. By understanding and implementing the proper configuration of GPIO pins, along with effective debouncing techniques, you can ensure stable and reliable switch readings in your embedded applications. This process is crucial for developing robust and responsive embedded systems.