110 lines
3.1 KiB
C
110 lines
3.1 KiB
C
/*
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* sr595.c:
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* Extend wiringPi with the 74x595 shift register as a GPIO
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* expander chip.
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* Note that the code can cope with a number of 595's
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* daisy-chained together - up to 4 for now as we're storing
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* the output "register" in a single unsigned int.
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*
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* Copyright (c) 2013 Gordon Henderson
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***********************************************************************
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* This file is part of wiringPi:
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* https://projects.drogon.net/raspberry-pi/wiringpi/
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*
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* wiringPi is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as
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* published by the Free Software Foundation, either version 3 of the
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* License, or (at your option) any later version.
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*
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* wiringPi is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with wiringPi.
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* If not, see <http://www.gnu.org/licenses/>.
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***********************************************************************
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*/
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#include <stdio.h>
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#include <stdint.h>
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#include "wiringPi.h"
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#include "sr595.h"
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/*
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* myDigitalWrite:
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*********************************************************************************
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*/
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static void myDigitalWrite (struct wiringPiNodeStruct *node, int pin, int value)
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{
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unsigned int mask ;
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int dataPin, clockPin, latchPin ;
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int bit, bits, output ;
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pin -= node->pinBase ; // Normalise pin number
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bits = node->pinMax - node->pinBase + 1 ; // ie. number of clock pulses
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dataPin = node->data0 ;
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clockPin = node->data1 ;
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latchPin = node->data2 ;
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output = node->data3 ;
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mask = 1 << pin ;
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if (value == LOW)
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output &= (~mask) ;
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else
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output |= mask ;
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node->data3 = output ;
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// A low -> high latch transition copies the latch to the output pins
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digitalWrite (latchPin, LOW) ; delayMicroseconds (1) ;
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for (bit = bits - 1 ; bit >= 0 ; --bit)
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{
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digitalWrite (dataPin, output & (1 << bit)) ;
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digitalWrite (clockPin, HIGH) ; delayMicroseconds (1) ;
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digitalWrite (clockPin, LOW) ; delayMicroseconds (1) ;
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}
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digitalWrite (latchPin, HIGH) ; delayMicroseconds (1) ;
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}
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/*
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* sr595Setup:
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* Create a new instance of a 74x595 shift register GPIO expander.
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*********************************************************************************
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*/
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int sr595Setup (const int pinBase, const int numPins,
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const int dataPin, const int clockPin, const int latchPin)
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{
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struct wiringPiNodeStruct *node ;
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node = wiringPiNewNode (pinBase, numPins) ;
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node->data0 = dataPin ;
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node->data1 = clockPin ;
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node->data2 = latchPin ;
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node->data3 = 0 ; // Output register
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node->digitalWrite = myDigitalWrite ;
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// Initialise the underlying hardware
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digitalWrite (dataPin, LOW) ;
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digitalWrite (clockPin, LOW) ;
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digitalWrite (latchPin, HIGH) ;
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pinMode (dataPin, OUTPUT) ;
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pinMode (clockPin, OUTPUT) ;
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pinMode (latchPin, OUTPUT) ;
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return TRUE ;
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}
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