LPC2148 – Keypad Interfacing

Last Updated on: June 29th, 2022

This article is a continuation of the series of tutorials on the LPC2148 Microcontroller (ARM7). The aim of this series is to provide easy and practical examples that anyone can understand. In the previous tutorial, we have interfaced the Relay with LPC2148 (ARM7). Now, we will see Keypad interfacing with LPC2148. Before that, I would suggest you to go through this link to know about the Keypad characteristics.  Let’s start…

Suggestion to read

• Matrix Keypad Operation
• Serial Communication

Components Required

• 4×4 Keypad or 3×4 Keypad (Here we will discuss both codes)
• LPC2148 Microcontroller

Keypad interfacing with LPC2148

4×4 Matrix Keypad Interfacing

Circuit Diagram

Keypad

• R1 – P1.16
• R2 – P1.17
• R3 – P1.18
• R4 – P1.19
• C1 – P1.20
• C2 – P1.21
• C3 – P1.22
• C4 – P1.23

Serial

• RX – P0.0
• TX – P0.1

Code 

This code might be looking complicate. Please go through this code slowly.

#include<lpc214x.h>

#define c1 (IOPIN1&1<<20)
#define c2 (IOPIN1&1<<21)
#define c3 (IOPIN1&1<<22)
#define c4 (IOPIN1&1<<23)

void ser_init(void);
void tx(unsigned char c);
unsigned char rx(void);
void tx_string(unsigned char *s);

unsigned char r_loc,c_loc;
unsigned char key[4][4]={"789/","456*","123-","C0=+"};
unsigned char keypad(void);

int main()
{
	IO1DIR=0x0f<<16;
	ser_init();
	while(1) {
		tx(keypad());
	}
}

unsigned char keypad()
{
	IO1PIN=0xf0<<16;

	while(c1 && c2 && c3 && c4);
	while(!c1 || !c2 || !c3 || !c4) {
		if(!c1 && c2 && c3 && c4)		c_loc=0;
		else if(c1 && !c2 && c3 && c4)	c_loc=1;
		else if(c1 && c2 && !c3 && c4)	c_loc=2;
		else if(c1 && c2 && c3 && !c4)	c_loc=3;

		IO1CLR = 1<<16;
		IO1SET = 0x0e<<16;
		if(!c1 || !c2 || !c3 || !c4) {
			r_loc=0;
			break;
		}

		IO1CLR = 1<<17;
		IO1SET = 0x0d<<16;
		if(!c1 || !c2 || !c3 || !c4) {
			r_loc=1;
			break;
		}

		IO1CLR = 1<<18;
		IO1SET = 0x0b<<16;
		if(!c1 || !c2 || !c3 || !c4)	{
			r_loc=2;
			break;
		}

		IO1CLR = 1<<19;
		IO1SET = 0x07<<16;
		if(!c1 || !c2 || !c3 || !c4)	{
			r_loc=3;
			break;
		}
	}
	while(!c1 || !c2 || !c3 || !c4);
	return (key[r_loc][c_loc]);
}

void ser_init()
{
	VPBDIV=0x02;					//PCLK = 30MHz
	PINSEL0=0x5;
	U0LCR=0x83;
	U0DLL=195;
	U0DLM=0;
	U0LCR=0x03;
	U0TER=(1<<7);
}

void tx(unsigned char c)
{
	U0THR=c;
	while((U0LSR&(1<<5))==0);
}

void tx_string(unsigned char *s)
{
	while(*s) {
		tx(*s++);
	}
}

unsigned char rx()
{
	while((U0LSR&(1<<0))==0);
	return U0RBR;
}	 

Output

Whatever we are typing in the keypad, it will send to the serial terminal.

3×4 Matrix Keypad Interfacing

Circuit Diagram

Keypad

• R1 – P1.16
• R2 – P1.17
• R3 – P1.18
• R4 – P1.19
• C1 – P1.20
• C2 – P1.21
• C3 – P1.22

Serial

• RX – P0.0
• TX – P0.1

Code

Whatever we are typing in the keypad, it will send to the serial terminal.

#include<lpc214x.h>

void ser_init(void);
void tx(unsigned char c);
unsigned char rx(void);
void tx_string(unsigned char *s);

#define c1 (IOPIN1&1<<20)
#define c2 (IOPIN1&1<<21)
#define c3 (IOPIN1&1<<22)

unsigned char r_loc,c_loc;
unsigned char key[4][3]={"123","456","789","*0#"};
unsigned char keypad(void);

int main()
{
	IO1DIR=0x0f<<16;
	ser_init();
	while(1) {
		tx(keypad());
	}
}

unsigned char keypad()
{
	IO1PIN=0xf0<<16;

	while(c1 && c2 && c3);
	while(!c1 || !c2 || !c3) {
		if(!c1 && c2 && c3)		c_loc=0;
		else if(c1 && !c2 && c3)	c_loc=1;
		else if(c1 && c2 && !c3)	c_loc=2;

		IO1CLR = 1<<16;
		IO1SET = 0x0e<<16;
		if(!c1 || !c2 || !c3) {
			r_loc=0;
			break;
		}

		IO1CLR = 1<<17;
		IO1SET = 0x0d<<16;
		if(!c1 || !c2 || !c3) {
			r_loc=1;
			break;
		}
		
		IO1CLR = 1<<18;
		IO1SET = 0x0b<<16;
		if(!c1 || !c2 || !c3) {
			r_loc=2;
			break;
		}

		IO1CLR = 1<<19;
		IO1SET = 0x07<<16;
		if(!c1 || !c2 || !c3) {
			r_loc=3;
			break;
		}
	}
	while(!c1 || !c2 || !c3);
	return (key[r_loc][c_loc]);
}

void ser_init()
{
	VPBDIV=0x02;					//PCLK = 30MHz
	PINSEL0=0x5;
	U0LCR=0x83;
	U0DLL=195;
	U0DLM=0;
	U0LCR=0x03;
	U0TER=(1<<7);
}

void tx(unsigned char c)
{
	U0THR=c;
	while((U0LSR&(1<<5))==0);
}

void tx_string(unsigned char *s)
{
	while(*s) {
		tx(*s++);
	}
}

unsigned char rx()
{
	while((U0LSR&(1<<0))==0);
	return U0RBR;
}

Output

In our next tutorial, we will see how to interface the GSM module with LPC2148 (ARM7). If you want to use FreeRTOS on LPC2148, then please refer FreeRTOS series.

You can also read the below tutorials.

Linux Device Driver Tutorials	C Programming Tutorials
FreeRTOS Tutorials	NuttX RTOS Tutorials
RTX RTOS Tutorials	Interrupts Basics
I2C Protocol – Part 1 (Basics)	I2C Protocol – Part 2 (Advanced Topics)
STM32 Tutorials	LPC2148 (ARM7) Tutorials
PIC16F877A Tutorials	8051 Tutorials
Unit Testing in C Tutorials	ESP32-IDF Tutorials
Raspberry Pi Tutorials	Embedded Interview Topics
Reset Sequence in ARM Cortex-M4	BLE Basics
VIC and NVIC in ARM	SPI – Serial Peripheral Interface Protocol
STM32F7 Bootloader Tutorials	Raspberry PI Pico Tutorials
STM32F103 Bootloader Tutorials	RT-Thread RTOS Tutorials
Zephyr RTOS Tutorials - STM32	Zephyr RTOS Tutorials - ESP32
VHDL Tutorials	UDS Protocol Tutorials
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