pocketbeagle i2c lcd, 16x2, hd44780,PCF8574

Thank you Shabaz. I have modified the code a bit, I have left those binary codes in the initialization as is, because, I find it helpful to simply cross check with datasheet of HD44780. I am leaving a modified version the code here, if anyone ever wants to use it.

/* ----------------------------------------------------------------------- *
 * Title:         pcf8574-lcd-demo                                         *
 * Description:   C-code for PCF8574T backpack controlling LCD through I2C *
 *                Tested on Raspberry Pi 3                                 *
 *                20180203 frank4dd                                        *
 *                                                                         *
 * Prerequisites: apt-get libi2c-dev i2c-tools                             *
 * Compilation:   gcc pcf8574-lcd-demo.c -o pcf8574-lcd-demo               *
 *------------------------------------------------------------------------ * 
 * PCF8574T backpack module uses 4-bit mode, LCD pins D0-D3 are not used.  *
 * backpack module wiring:                                                 *
 *                                                                         *
 *  PCF8574T     LCD                                                       *
 *  ========     ======                                                    *
 *     P0        RS                                                        *
 *     P1        RW                                                        *
 *     P2        Enable                                                    *
 *     P3        Led Backlight                                             *
 *     P4        D4                                                        *
 *     P5        D5                                                        *
 *     P6        D6                                                        *
 *     P7        D7                                                        *
 *                                                                         *
 * I2C-byte: D7 D6 D5 D4 BL EN RW RS                                       *
 * ----------------------------------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#include <fcntl.h>
#include <sys/ioctl.h>




#define I2C_BUS        "/dev/i2c-2" // I2C bus device on a Raspberry Pi 3
#define I2C_ADDR       0x27         // I2C slave address for the LCD module
#define NUMBER_OF_CHAR_PER_LINE 16
#define NUMBER_OF_LINE 2
int lcd_backlight;
int debug;
char address;
char out[4];
int i2cFile;
int cursor_pos;








void i2c_start() {
   if((i2cFile = open(I2C_BUS, O_RDWR)) < 0) {
      printf("Error failed to open I2C bus [%s].\n", I2C_BUS);
      exit(-1);
   }
   // set the I2C slave address for all subsequent I2C device transfers
   if (ioctl(i2cFile, I2C_SLAVE, I2C_ADDR) < 0) {
      printf("Error failed to set I2C address [%s].\n", I2C_ADDR);
      exit(-1);
   }
}


void i2c_stop() { close(i2cFile); }










char convert_to_nibbels(char foo) { 

char n1,n2,ln1,ln2,mask1,mask2,out1,out2,out3,out4;


ln1 = 0b11111101;
ln2 = 0b11111001;


mask1 = 0b11110000;
mask2 = 0b00001111;


n1 = foo & mask1;
n1 = n1 | mask2;
//printf("n1 is : 0x%x \r\n",n1);


n2 = foo & mask2;
n2 = n2<<4;      
n2 = n2 | mask2;
//printf("n2 is : 0x%x \r\n",n2);






out1 = n1 & ln1 ;
//printf("out1 is : 0x%x \r\n",out1);
out2 = n1 & ln2;
//printf("out2 is : 0x%x \r\n",out2);


out3 = n2 & ln1 ;
//printf("out3 is : 0x%x \r\n",out3);
out4 = n2 & ln2 ;
//printf("out4 is : 0x%x \r\n",out4);
out[0] = out1;
out[1] = out2;
out[2] = out3;
out[3] = out4;

}
char convert_cmd_to_nibbels(char foo) { 

char n1,n2,ln1,ln2,mask1,mask2,out1,out2,out3,out4;


ln1 = 0b11111100;
ln2 = 0b11111000;


mask1 = 0b11110000;
mask2 = 0b00001111;


n1 = foo & mask1;
n1 = n1 | mask2;
//printf("n1 is : 0x%x \r\n",n1);


n2 = foo & mask2;
n2 = n2<<4;      
n2 = n2 | mask2;
//printf("n2 is : 0x%x \r\n",n2);






out1 = n1 & ln1 ;
//printf("out1 is : 0x%x \r\n",out1);
out2 = n1 & ln2;
//printf("out2 is : 0x%x \r\n",out2);


out3 = n2 & ln1 ;
//printf("out3 is : 0x%x \r\n",out3);
out4 = n2 & ln2 ;
//printf("out4 is : 0x%x \r\n",out4);
out[0] = out1;
out[1] = out2;
out[2] = out3;
out[3] = out4;

}








void i2c_send_byte(unsigned char data) {
   unsigned char byte[1];
   byte[0] = data;
   write(i2cFile, byte, sizeof(byte)); 
   /* -------------------------------------------------------------------- *
    * Below wait creates 1msec delay, needed by display to catch commands  *
    * -------------------------------------------------------------------- */
   usleep(000);
}




void clear_display()
{
   /* -------------------------------------------------------------------- *
    * Display clear, cursor home                                           *
    * -------------------------------------------------------------------- */
   usleep(40);                // wait 40usec
   i2c_send_byte(0b00000100); //
   i2c_send_byte(0b00000000); // D7-D4=0
   i2c_send_byte(0b00010100); //
   i2c_send_byte(0b00010000); // D0=display_clear


   /* -------------------------------------------------------------------- *
    * Turn on the display                                                  *
    * -------------------------------------------------------------------- */
   usleep(40);                // wait 40usec
   i2c_send_byte(0b00001100); //
   i2c_send_byte(0b00001000); // D7-D4=0
   i2c_send_byte(0b11101100); //
   i2c_send_byte(0b11101000); // D3=1 D2=display_on, D1=cursor_on, D0=cursor_blink
   cursor_pos =1 ;
}




void send_cmd_char_to_lcd(char foo)
{
int i;
convert_cmd_to_nibbels(foo);
for(i=0;i<4;i++)
{
   i2c_send_byte(out[i]);
}
}


void go_to(int line, char position)
{
if(line==1)
{
cursor_pos = position;
position = 0x80+position;
}
else if(line==2)
{
cursor_pos = position+40;
position = 0xC0+position;
}
send_cmd_char_to_lcd(position);
}


void send_char_to_lcd(char foo)
{
int i;
convert_to_nibbels(foo);
for(i=0;i<4;i++)
{
   i2c_send_byte(out[i]);
}
   cursor_pos++;
}


void send_string_to_lcd(int argc,char *str[])
{


int i, counter;
for(counter=1;counter<argc;counter++)
{
for(i=0;str[counter][i]!=0x00;i++)
{ 
   send_char_to_lcd(str[counter][i]);
   if(cursor_pos==(NUMBER_OF_CHAR_PER_LINE+1))
{
   go_to(2,0);  
}
}
}
}


void send_simple_string_to_lcd(char *str)
{


int i;
for(i=0;(str[i]!=0x00);i++)
{
    send_char_to_lcd(str[i]);
}


}




void main(int argc, char* argv[]) { 
   i2c_start(); 
   debug=1;
   cursor_pos =1 ;



   /* -------------------------------------------------------------------- *
    * Initialize the display, using the 4-bit mode initialization sequence *
    * -------------------------------------------------------------------- */
  // if(debug) printf("Init Start:\n");
  // if(debug) printf("D7 D6 D5 D4 BL EN RW RS\n");




if(argv[1][0] =='R')
{


   sleep(0.4);             // wait 40msec
   i2c_send_byte(0b00110100); // D7=0, D6=0, D5=1, D4=1, RS,RW=0 EN=1
   i2c_send_byte(0b00110000); // D7=0, D6=0, D5=1, D4=1, RS,RW=0 EN=0


   sleep(0.1);              // wait 10msec
   i2c_send_byte(0b00110100); // 
   i2c_send_byte(0b00110000); // same
   sleep(0.1);               // wait 10msec
   i2c_send_byte(0b00110100); //
   i2c_send_byte(0b00110000); // 8-bit mode init complete
   sleep(0.1);              // wait 10msec
   i2c_send_byte(0b00100100); //
   i2c_send_byte(0b00100000); // switched now to 4-bit mode




   /* -------------------------------------------------------------------- *
    * 4-bit mode initialization complete. Now configuring the function set *
    * -------------------------------------------------------------------- */
   usleep(100);                // wait 100usec
   i2c_send_byte(0b00100100); //
   i2c_send_byte(0b00100000); // keep 4-bit mode
   i2c_send_byte(0b10000100); //
   i2c_send_byte(0b10000000); // D3=2lines, D2=char5x8


   /* -------------------------------------------------------------------- *
    * Next turn display off                                                *
    * -------------------------------------------------------------------- */
   usleep(100);                // wait 100usec
   i2c_send_byte(0b00000100); //
   i2c_send_byte(0b00000000); // D7-D4=0
   i2c_send_byte(0b10000100); //
   i2c_send_byte(0b10000000); // D3=1 D2=display_off, D1=cursor_off, D0=cursor_blink


   /* -------------------------------------------------------------------- *
    * Display clear, cursor home                                           *
    * -------------------------------------------------------------------- */
   usleep(100);                // wait 100usec
   i2c_send_byte(0b00000100); //
   i2c_send_byte(0b00000000); // D7-D4=0
   i2c_send_byte(0b00010100); //
   i2c_send_byte(0b00010000); // D0=display_clear


   /* -------------------------------------------------------------------- *
    * Set cursor direction                                                 *
    * -------------------------------------------------------------------- */
   usleep(100);                // wait 100usec
   i2c_send_byte(0b00000100); //
   i2c_send_byte(0b00000000); // D7-D4=0
   i2c_send_byte(0b01100100); //
   i2c_send_byte(0b01100000); // print left to right


   /* -------------------------------------------------------------------- *
    * Turn on the display                                                  *
    * -------------------------------------------------------------------- */
   usleep(100);                // wait 100usec
   i2c_send_byte(0b00001100); //
   i2c_send_byte(0b00001000); // D7-D4=0
   i2c_send_byte(0b11101100); //
   i2c_send_byte(0b11101000); // D3=1 D2=display_on, D1=cursor_on, D0=cursor_blink


   sleep(1);


}
else if (argv[1][0] == 'c')
{
clear_display();
}
else
{
    //  send_string_to_lcd(argc,argv);
   //   go_to(2,0);
   //   send_cmd_char_to_lcd(0x0C); // cursor off 
send_simple_string_to_lcd("SET P : 300");
go_to(2,0);
send_simple_string_to_lcd("CURRENT P : ");


}


   i2c_stop(); 
}

Hi chris,

Can you explain how convert into nibbles function works?

Hi chris,

Can you explain how convert into nibbles function works?