Hi All, I am trying the below code with hd44780 display an pcf8574. I can control the backlight so i2c is working, but all the below code does, flickers the backlight and comes back to a blank screen.
Can anyone confirm if the commands are correct ?. Thanks
/* ----------------------------------------------------------------------- *
* 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 BINARY_FORMAT " %c %c %c %c %c %c %c %c\n"
#define BYTE_TO_BINARY(byte) \
(byte & 0x80 ? '1' : '0'), \
(byte & 0x40 ? '1' : '0'), \
(byte & 0x20 ? '1' : '0'), \
(byte & 0x10 ? '1' : '0'), \
(byte & 0x08 ? '1' : '0'), \
(byte & 0x04 ? '1' : '0'), \
(byte & 0x02 ? '1' : '0'), \
(byte & 0x01 ? '1' : '0')
int lcd_backlight;
int debug;
char address;
int i2cFile;
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); }
void i2c_send_byte(unsigned char data) {
unsigned char byte[1];
byte[0] = data;
if(debug) printf(BINARY_FORMAT, BYTE_TO_BINARY(byte[0]));
write(i2cFile, byte, sizeof(byte));
/* -------------------------------------------------------------------- *
* Below wait creates 1msec delay, needed by display to catch commands *
* -------------------------------------------------------------------- */
usleep(000);
}
void main() {
i2c_start();
debug=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");
usleep(30000); // wait 15msec
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
usleep(8200); // wait 4.1msec
i2c_send_byte(0b00110100); //
i2c_send_byte(0b00110000); // same
usleep(200); // wait 100usec
i2c_send_byte(0b00110100); //
i2c_send_byte(0b00110000); // 8-bit mode init complete
usleep(8200); // wait 4.1msec
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(80); // wait 40usec
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(80); // wait 40usec
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(80); // wait 40usec
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(80); // wait 40usec
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(80); // 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
if(debug) printf("Init End.\n");
sleep(1);
if(debug) printf("Writing HELLO to display\n");
if(debug) printf("D7 D6 D5 D4 BL EN RW RS\n");
#if 1
/* -------------------------------------------------------------------- *
* Start writing 'H' 'E' 'L' 'L' 'O' chars to the display, with BL=on. *
* -------------------------------------------------------------------- */
i2c_send_byte(0b01001101); //
i2c_send_byte(0b01001001); // send 0100=4
i2c_send_byte(0b10001101); //
i2c_send_byte(0b10001001); // send 1000=8 = 0x48 ='H'
i2c_send_byte(0b01001101); //
i2c_send_byte(0b01001001); // send 0100=4
i2c_send_byte(0b01011101); //
i2c_send_byte(0b01011001); // send 0101=1 = 0x41 ='E'
i2c_send_byte(0b01001101); //
i2c_send_byte(0b01001001); // send 0100=4
i2c_send_byte(0b11001101); //
i2c_send_byte(0b11001001); // send 1100=12 = 0x4D ='L'
i2c_send_byte(0b01001101); //
i2c_send_byte(0b01001001); // send 0100=4
i2c_send_byte(0b11001101); //
i2c_send_byte(0b11001001); // send 1100=12 = 0x4D ='L'
i2c_send_byte(0b01001101); //
i2c_send_byte(0b01001001); // send 0100=4
i2c_send_byte(0b11111101); //
i2c_send_byte(0b11111001); // send 1111=15 = 0x4F ='O'
#endif
if(debug) printf("Finished writing to display.\n");
i2c_stop();
}
