PIC16F887 SPI MCP23S17 Character LCD and KeyPad XC8 Example

In previous example, I use the MCP23S17 to drive an HD44780 based 20x4 character LCD using the 4-bit data transfer mode. This chip has two GPIO ports. So it can interface to various types of digital I/O devices including a dot matrix display, a multiplexing 7-Segment display, a matrix keypad, etc.

Simulating Program in Proteus

In this example, I use a 20x4 character LCD and a 4x4 matrix keypad. They are controlled by the MCP23S17 GPIO extender chip. This chip uses the SPI interface that controlled by a PIC16F887 micro-controller. 

A 4x4 membrane matrix keypad is suitable for most of hobbyist electronics projects

I add a key pad scanning routine in the C main file. It's very simple, and light weight. The founded key is an ASCII character that directly show on the LCD, otherwise it return 0 value.

/*
 * File:   main.c
 * Author: Admin
 *
 * Created on February 11, 2024, 10:42 AM
 */
 
#include <xc.h>
#include "config.h"
#include "mcp23S17.h"
 
#define _XTAL_FREQ  8000000UL
 
/*MCP23S17 4x4 KeyPad Scan Function*/
const uint8_t key_ascii[][4]={
'7','8','9','/',
'4','5','6','*',
'1','2','3','-',
'x','0','=','+'
};
uint8_t get_key(void);
 
void main(void) {
    uint8_t key=0,char_count=0, new_line=0,line_num=1;
    OSCCONbits.IRCF=7;
    lcd_init();
    lcd_text("PIC16F887   MCP23S17");
    lcd_xy(1,2); lcd_text("Character LCD KeyPad");
    lcd_xy(1,3); lcd_text("Example Using MPLABX");
    lcd_xy(1,4); lcd_text("IDE And XC8 Compiler");
    __delay_ms(3000);
    lcd_clear();
    while(1){
        key=get_key();
        if(key!=0){
            lcd_data(key);
            __delay_ms(250);
            char_count+=1;
        }
        if(char_count>=20){char_count=0; new_line=1;}
        if(new_line){
            new_line=0;
            line_num+=1;
            switch(line_num){
                case 2: lcd_xy(1,2); break;
                case 3: lcd_xy(1,3); break;
                case 4: lcd_xy(1,4); break;
                case 5: lcd_clear(); line_num=1; break;
            }
        }
    }
}
 
uint8_t get_key(void){
    uint8_t data,key_value=0;
    for(uint8_t i=0;i<4;i++){
        mcp23S17_send(OLATB,1<<i);
        __delay_ms(10);
        data=mcp23S17_receive(GPIOB);
        data=data>>4;
        if(data==0x01) {key_value=key_ascii[i][0]; break;}
        else if(data==0x02) {key_value=key_ascii[i][1]; break;}
        else if(data==0x04) {key_value=key_ascii[i][2]; break;}
        else if(data==0x08) {key_value=key_ascii[i][3]; break;}
        else key_value=0;
    }
    return key_value;
}

I wrote a driver for the MCP23S17 that use the SPI driver within the project file.

The mcp23S17.h C header file:

/* 
 * File:   mcp23S17.h
 * Author: Admin
 *
 * Created on February 9, 2024, 3:54 PM
 */
 
#include <xc.h>
#include "spi.h"
 
/*MCP23S17 Registers Definition*/
#define IODIRA      0x00
#define IODIRB      0x01
#define IPOLA       0x02
#define IPOLB       0x03
#define GPINTENA    0x04
#define GPINTENB    0x05
#define DEFVALA     0x06
#define DEFVALB     0x07
#define INTCONA     0x08
#define INTCONB     0x09
#define IOCONA      0x0A
#define IOCONB      0x0B
#define GPPUA       0x0C
#define GPPUB       0x0D
#define INTFA       0x0E
#define INTFB       0x0F
#define INTCAPA     0x10
#define INTCAPB     0x11
#define GPIOA       0x12
#define GPIOB       0x13
#define OLATA       0x14
#define OLATB       0x15
 
/*MCP23S17 Address*/
#define WRITE_ADDR  0x40
#define READ_ADDR   0x41
 
/*MCP23S17 Read and Write Functions*/
void mcp23S17_send(uint8_t address, uint8_t data);
uint8_t mcp23S17_receive(uint8_t address);
 
/*MCP23S17 Character LCD Functions*/
#define RS  0
#define EN  2
void lcd_command(uint8_t command);
void lcd_data(uint8_t myChar);
void lcd_xy(uint8_t x, uint8_t y);
void lcd_text(uint8_t *txt);
void lcd_clear(void);
void lcd_init(void);
 
 

The mcp23S17.c C source file:

 
#include "mcp23S17.h"
 
/*MCP23S17 Input Output Functions*/
void mcp23S17_send(uint8_t address, uint8_t data){
    nCS=0;
    spi_send(WRITE_ADDR);
    spi_send(address);
    spi_send(data);
    nCS=1;
}
 
uint8_t mcp23S17_receive(uint8_t address){
    uint8_t data;
    nCS=0;
    spi_send(READ_ADDR);
    spi_send(address);
    data=spi_receive();
    nCS=1;  
    return data;
}
 
/*MCP23S17 Character LCD Functions*/
void delay(uint16_t count){
    while(count>0) count--;
}
void lcd_command(uint8_t command){
    uint8_t data;
    data=command&0xF0;
    mcp23S17_send(OLATA, data|(1<<EN));
    delay(50);
    mcp23S17_send(OLATA, data);
    delay(50);
 
    data=command<<4;
    mcp23S17_send(OLATA, data|(1<<EN));
    delay(50);
    mcp23S17_send(OLATA, data);
    delay(50);
}
 
void lcd_data(uint8_t myChar){
    uint8_t data;
    data=myChar&0xF0;
    mcp23S17_send(OLATA, data|(1<<RS)|(1<<EN));
    delay(50);
    mcp23S17_send(OLATA, data);
    delay(50);
 
    data=myChar<<4;
    mcp23S17_send(OLATA, data|(1<<RS)|(1<<EN));
    delay(50);
    mcp23S17_send(OLATA, data|(1<<RS));
    delay(50);
}
 
void lcd_xy(uint8_t x, uint8_t y){
    /*20x4 Character LCD*/
    uint8_t tbe[]={0x80,0xC0,0x94,0xD4};
    lcd_command(tbe[y-1]+x-1);
}
 
void lcd_text(uint8_t *txt){
    while(*txt) lcd_data(*txt++);
}
 
void lcd_init(void){
    spi_init();
    nCS=1;
    /*LCD PORT*/
    mcp23S17_send(IODIRA,0x00);
    mcp23S17_send(OLATA,0x00);
    /*KeyPad PORT*/
    mcp23S17_send(IODIRB,0xF0);
 
    lcd_command(0x33);
    lcd_command(0x32);
    lcd_command(0x28);
    lcd_command(0x0F);
    lcd_command(0x01);
    delay(500);
    lcd_command(0x06);
}
 
void lcd_clear(void){
    lcd_command(0x01);
    delay(500);
}
 
 

Simulating Program

Click here to download its source file.