sr595.c
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/*
* sr595.c:
* Extend wiringPi with the 74x595 shift register as a GPIO
* expander chip.
* Note that the code can cope with a number of 595's
* daisy-chained together - up to 4 for now as we're storing
* the output "register" in a single unsigned int.
*
* 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 <stdio.h>
#include <stdint.h>
#include "wiringPi.h"
#include "sr595.h"
/*
* myDigitalWrite:
*********************************************************************************
*/
static void myDigitalWrite (struct wiringPiNodeStruct *node, int pin, int value)
{
unsigned int mask ;
int dataPin, clockPin, latchPin ;
int bit, bits, output ;
pin -= node->pinBase ; // Normalise pin number
bits = node->pinMax - node->pinBase + 1 ; // ie. number of clock pulses
dataPin = node->data0 ;
clockPin = node->data1 ;
latchPin = node->data2 ;
output = node->data3 ;
mask = 1 << pin ;
if (value == LOW)
output &= (~mask) ;
else
output |= mask ;
node->data3 = output ;
// A low -> high latch transition copies the latch to the output pins
digitalWrite (latchPin, LOW) ; delayMicroseconds (1) ;
for (bit = bits - 1 ; bit >= 0 ; --bit)
{
digitalWrite (dataPin, output & (1 << bit)) ;
digitalWrite (clockPin, HIGH) ; delayMicroseconds (1) ;
digitalWrite (clockPin, LOW) ; delayMicroseconds (1) ;
}
digitalWrite (latchPin, HIGH) ; delayMicroseconds (1) ;
}
/*
* sr595Setup:
* Create a new instance of a 74x595 shift register GPIO expander.
*********************************************************************************
*/
int sr595Setup (const int pinBase, const int numPins,
const int dataPin, const int clockPin, const int latchPin)
{
struct wiringPiNodeStruct *node ;
node = wiringPiNewNode (pinBase, numPins) ;
node->data0 = dataPin ;
node->data1 = clockPin ;
node->data2 = latchPin ;
node->data3 = 0 ; // Output register
node->digitalWrite = myDigitalWrite ;
// Initialise the underlying hardware
digitalWrite (dataPin, LOW) ;
digitalWrite (clockPin, LOW) ;
digitalWrite (latchPin, HIGH) ;
pinMode (dataPin, OUTPUT) ;
pinMode (clockPin, OUTPUT) ;
pinMode (latchPin, OUTPUT) ;
return 0 ;
}