pcf8591.c
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/*
* pcf8591.c:
* Extend wiringPi with the PCF8591 I2C GPIO Analog expander chip
* The chip has 1 8-bit DAC and 4 x 8-bit ADCs
* Copyright (c) 2013 Gordon Henderson
***********************************************************************
* This file is part of wiringPi:
* https://projects.drogon.net/raspberry-pi/wiringpi/
*
* wiringPi is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* wiringPi is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with wiringPi.
* If not, see <http://www.gnu.org/licenses/>.
***********************************************************************
*/
#include <unistd.h>
#include "wiringPi.h"
#include "wiringPiI2C.h"
#include "pcf8591.h"
/*
* myAnalogWrite:
*********************************************************************************
*/
static void myAnalogWrite (struct wiringPiNodeStruct *node, int pin, int value)
{
unsigned char b [2] ;
b [0] = 0x40 ;
b [1] = value & 0xFF ;
write (node->fd, b, 2) ;
}
/*
* myAnalogRead:
*********************************************************************************
*/
static int myAnalogRead (struct wiringPiNodeStruct *node, int pin)
{
int x ;
wiringPiI2CWrite (node->fd, 0x40 | ((pin - node->pinBase) & 3)) ;
x = wiringPiI2CRead (node->fd) ; // Throw away the first read
x = wiringPiI2CRead (node->fd) ;
return x ;
}
/*
* pcf8591Setup:
* Create a new instance of a PCF8591 I2C GPIO interface. We know it
* has 4 pins, (4 analog inputs and 1 analog output which we'll shadow
* input 0) so all we need to know here is the I2C address and the
* user-defined pin base.
*********************************************************************************
*/
int pcf8591Setup (const int pinBase, const int i2cAddress)
{
int fd ;
struct wiringPiNodeStruct *node ;
if ((fd = wiringPiI2CSetup (i2cAddress)) < 0)
return fd ;
node = wiringPiNewNode (pinBase, 4) ;
node->fd = fd ;
node->analogRead = myAnalogRead ;
node->analogWrite = myAnalogWrite ;
return 0 ;
}