/* 
    PCF8574_addr_byteout_slug.c
    ---------------------------
    Send address and byte to switch lines on 8 line port of i2c bus PCF8574
    -----------------------------------------------------------------------
 
      1) send the i2c address
      2) send byte to set the 8 port lines on or off

  usage :-  type with spaces but without the < >
<PCF8574_addr_byteout_slug>  <decimal address> <decimal byte out  0-255>

*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#define I2C_SLAVE	0x0703	/* Change slave address	*/

  int i2c;
  char filename[20];
  unsigned long address;

  int rc;
  unsigned char data[1];


int main(int argc, char *argv[]) 
{
  if (argc != 3) {  /* error if we are not getting just 2 inputs after the program name */
    fprintf(stderr, "usage: %s <address> <databyte>\n",argv[0]);
    exit(1);
}  

  /* address is the first number after the program name */
  address = atoi(argv[1]);
  /* the byte to send out to the PC8574 is the second number
     place it into the first element of the buf array */
  data[0] = atoi(argv[2]);

  i2c = open("/dev/i2c-0",O_RDWR); /* open the device dev/i2c-0 */

  rc=ioctl(i2c,I2C_SLAVE,address); /* set the i2c chip address */

  write(i2c,data,1) ; /* send the byte */

  i2c = close(i2c);
  return(0);
}