ATMega32 SPI Interfaces To SN74HC164 And LCD Using 3 Pins

The HD44780 character LCD type uses parallel interface with controller, even it operates in 4-bit data transfer mode. Currently most electronic hobbyists use an additional shift register or an I/O expanding chip, especially the PCF8574T chip.

Character LCD With PCF8574T

In this example, I use SN74HC164 shift register to interface between controller and character LCD. 

Schematic Diagram

I use two wires - serial data and serial clock to interface between controller and SN74HC164. However I use one additional pin to interacts with LCD Enable pin. It's because I have difficulty during programming.

/*
 * SPI74164LCD.c
 *
 * Created: 7/7/2023 9:48:09 AM
 * Author : Admin
 */ 
 
 
#include <avr/io.h>
 
#define F_CPU 4000000UL
#include <util/delay.h>
 
void masterInit(void){
	/*Set MOSI, SCK and SS Output*/
	DDRB|=(1<<4)|(1<<5)|(1<<7);
	/*Enable SPI Master Set Clock Rate Fclk/4*/
	SPCR|=(1<<SPE)|(1<<MSTR);
}
 
void masterTransmit(unsigned char spiData){
	/*Start The Transmission*/
	SPDR = spiData;
	/*Wait For Completion*/
	while(!(SPSR&(1<<SPIF)));
}
 
void lcdCmd(unsigned char cmd){
 
	masterTransmit(cmd&0xF0);
	PORTB|=(1<<4);
	_delay_us(100);
	PORTB&=~(1<<4);
	_delay_us(100);
 
	masterTransmit(cmd<<4);
	PORTB|=(1<<4);
	_delay_us(100);
	PORTB&=~(1<<4);
	_delay_us(100);
 
}
 
void lcdDat(unsigned char dat){
 
	masterTransmit((dat&0xF0)|1);
	PORTB|=(1<<4);
	_delay_us(100);
	PORTB&=~(1<<4);
	_delay_us(100);
 
	masterTransmit((dat<<4)|1);
	PORTB|=(1<<4);
	_delay_us(100);
	PORTB&=~(1<<4);
	_delay_us(100);
}
 
void lcdInit(){
 
	masterTransmit(0x00);
	_delay_ms(20);
	lcdCmd(0x33);
	_delay_us(100);
	lcdCmd(0x32);
	_delay_us(100);
	lcdCmd(0x28);
	_delay_us(100);
 
	lcdCmd(0x0F);
	_delay_us(100);
	lcdCmd(0x01);
	_delay_ms(2);
	lcdCmd(0x06);
	_delay_us(100);
}
 
void lcdStr( char *str){
	unsigned char i=0;
	while(str[i]!=0){
		lcdDat(str[i]);
		i++;
	}
}
 
void lcdXY(unsigned char x, unsigned char y){
	unsigned char tbe[]={0x80,0xC0,0x94,0xD4};	// 20x4
	lcdCmd(tbe[y-1]+x-1);
	_delay_us(100);
}
 
void lcdClear(){
	lcdCmd(0x01);
	_delay_us(10);
}
 
 
int main(void)
{
    masterInit();
 
	lcdInit();
 
	lcdXY(1,1);
	lcdStr("ATMEGA32 SN74HC164");
 
	lcdXY(1,2);
	lcdStr("Character LCD ");
	lcdXY(1,3);
	lcdStr("Interfacing Using");
	lcdXY(1,4);
	lcdStr("Three Wires.......");
	lcdCmd(0x0F);
	_delay_ms(100);
 
    while (1) 
    {				
    }
}
 
 
 

Click here to download source file.

Simulating Program