112 lines
2.6 KiB
C
112 lines
2.6 KiB
C
/*
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twi.c - Stripped-down TWI/I2C library
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Copyright (c) 2006 Nicholas Zambetti. All right reserved.
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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Modified 2012 by Todd Krein (todd@krein.org) to implement repeated starts
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*/
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#include <math.h>
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#include "Arduino.h" // for digitalWrite
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#ifndef cbi
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#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
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#endif
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#ifndef sbi
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#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
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#endif
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#include "twi.h"
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void twi_init(void)
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{
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// activate internal pullups for twi.
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digitalWrite(SDA, 1);
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digitalWrite(SCL, 1);
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// initialize twi prescaler and bit rate
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cbi(TWSR, TWPS0);
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cbi(TWSR, TWPS1);
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TWBR = ((F_CPU / TWI_FREQ) - 16) / 2;
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/* twi bit rate formula from atmega128 manual pg 204
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SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
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note: TWBR should be 10 or higher for master mode
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It is 72 for a 16mhz Wiring board with 100kHz TWI */
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}
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void twi_disable(void)
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{
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// deactivate internal pullups for twi.
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digitalWrite(SDA, 0);
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digitalWrite(SCL, 0);
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}
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static void twi_wait()
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{
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while(!(TWCR & _BV(TWINT)));
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}
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uint8_t twi_rw8(uint8_t address, uint8_t mode, uint8_t* data)
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{
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// send start condition
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TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTA);
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twi_wait();
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if(TW_STATUS != TW_START)
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return 1;
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// send address
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TWDR = mode;
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TWDR |= (address << 1);
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TWCR = _BV(TWEN) | _BV(TWINT);
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twi_wait();
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if(mode == TW_WRITE)
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{
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if(TW_STATUS != TW_MT_SLA_ACK)
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return 2;
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// send data
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TWDR = *data;
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TWCR = _BV(TWEN) | _BV(TWINT);
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twi_wait();
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if(TW_STATUS != TW_MT_DATA_ACK)
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return 3;
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}
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else
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{
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if(TW_STATUS != TW_MR_SLA_ACK)
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return 2;
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// receive data
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TWCR = _BV(TWEN) | _BV(TWINT);
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twi_wait();
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// accept ACK or NACK (since only 1 byte is read)
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if(!(TW_STATUS & TW_MR_DATA_ACK))
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return 3;
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*data = TWDR;
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}
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// send stop
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TWCR = _BV(TWEN) | _BV(TWINT) | _BV(TWSTO);
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return 0;
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}
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