First of all: Do not use Wiring. It, while well intentioned, does not do what it should. I have appropriated a chunk of code from the avrlibc library (http://www.nongnu.org/avr-libc/)
An excerpt from my thesis notes:
« What I don’t like about Wire is that it’s abstracting too much, and won’t let me write in the same protocol that every I2C data sheet I’ve seen speaks… How the devil do you send a restart? An end and a new start? Isn’t that sending a stop? I suspect this is my problem.
So, I’ll be looking to port a much more reliable library, probably something from the avr-libc community. Let’s see how tough it is. »
Some quick notes for the Arduino Mini: Analog 4: SDA (connect to pin 4 on color sensor) Analog 5: SCL (connect to pin 6 on color sensor)
*Don’t forget that both lines need to have a pull-up resistor of about 4.7k.
I’ve created a file named TWI_Hack.c, and I include it at the top of my arduino sketch. In that file, I have the following:
NB : This is depreciated. Use at your own risk. It once worked for me, and worked long enough to finish a bunch of school projects. Now that Arduino has released a few new models, and due to me now having a full time job that sadly isn’t playing with microprocessors, I haven’t touched, tried, or updated this since 2008. In the meantime, wiring might be a better option if it’s come along, or has more working examples.
-d
//------TWI_Hack.c
//Mangling by Dylan Moore to get avr-libc's i2c communication going with arduino
/* define CPU frequency in Mhz here if not defined in Makefile */
#ifndef F_CPU
#define F_CPU 4000000UL
#endif
/** defines the data direction (reading from I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_READ 1
/** defines the data direction (writing to I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_WRITE 0
/* I2C clock in Hz */
#define SCL_CLOCK 100000L
//Defines from Marek Michalkiewicz's awesome TWI.h
/* TWSR values (not bits) */
/* Master */
#define TW_START 0x08
#define TW_REP_START 0x10
/* Master Transmitter */
#define TW_MT_SLA_ACK 0x18
#define TW_MT_SLA_NACK 0x20
#define TW_MT_DATA_ACK 0x28
#define TW_MT_DATA_NACK 0x30
#define TW_MT_ARB_LOST 0x38
/* Master Receiver */
#define TW_MR_ARB_LOST 0x38
#define TW_MR_SLA_ACK 0x40
#define TW_MR_SLA_NACK 0x48
#define TW_MR_DATA_ACK 0x50
#define TW_MR_DATA_NACK 0x58
/* Slave Transmitter */
#define TW_ST_SLA_ACK 0xA8
#define TW_ST_ARB_LOST_SLA_ACK 0xB0
#define TW_ST_DATA_ACK 0xB8
#define TW_ST_DATA_NACK 0xC0
#define TW_ST_LAST_DATA 0xC8
/* Slave Receiver */
#define TW_SR_SLA_ACK 0x60
#define TW_SR_ARB_LOST_SLA_ACK 0x68
#define TW_SR_GCALL_ACK 0x70
#define TW_SR_ARB_LOST_GCALL_ACK 0x78
#define TW_SR_DATA_ACK 0x80
#define TW_SR_DATA_NACK 0x88
#define TW_SR_GCALL_DATA_ACK 0x90
#define TW_SR_GCALL_DATA_NACK 0x98
#define TW_SR_STOP 0xA0
/* Misc */
#define TW_NO_INFO 0xF8
#define TW_BUS_ERROR 0x00
/* The lower 3 bits of TWSR are reserved on the ATmega163.
* The 2 LSB carry the prescaler bits on the newer ATmegas. */
#define TW_STATUS_MASK (_BV(TWS7)|_BV(TWS6)|_BV(TWS5)|_BV(TWS4)|\
_BV(TWS3))
#define TW_STATUS (TWSR & TW_STATUS_MASK)
/* R/~W bit in SLA+R/W address field.*/
#define TW_READ 1
#define TW_WRITE 0
//Functions:
//Amazingly awesome I2C library written by Peter Fleury!
/*************************************************************************
Initialization of the I2C bus interface. Need to be called only once
*************************************************************************/
void i2c_init(void)
{
/* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
TWSR = 0; /* no prescaler */
TWBR = ((F_CPU/SCL_CLOCK)-16)/2; /* must be > 10 for stable operation */
}/* i2c_init */
/*************************************************************************
Issues a start condition and sends address and transfer direction.
return 0 = device accessible, 1= failed to access device
*************************************************************************/
unsigned char i2c_start(unsigned char address)
{
uint8_t twst;
// send START condition
TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
// wait until transmission completed
while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst != TW_START) && (twst != TW_REP_START)) return 1;
// send device address
TWDR = address;
TWCR = (1<<TWINT) | (1<<TWEN);
// wail until transmission completed and ACK/NACK has been received
while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1;
return 0;
}/* i2c_start */
/*************************************************************************
Issues a start condition and sends address and transfer direction.
If device is busy, use ack polling to wait until device is ready
Input: address and transfer direction of I2C device
*************************************************************************/
void i2c_start_wait(unsigned char address)
{
uint8_t twst;
while ( 1 )
{
// send START condition
TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
// wait until transmission completed
while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst != TW_START) && (twst != TW_REP_START)) continue;
// send device address
TWDR = address;
TWCR = (1<<TWINT) | (1<<TWEN);
// wail until transmission completed
while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits.
twst = TW_STATUS & 0xF8;
if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) )
{
/* device busy, send stop condition to terminate write operation */
TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
// wait until stop condition is executed and bus released
while(TWCR & (1<<TWSTO));
continue;
}
//if( twst != TW_MT_SLA_ACK) return 1;
break;
}
}/* i2c_start_wait */
/*************************************************************************
Issues a repeated start condition and sends address and transfer direction
Input: address and transfer direction of I2C device
Return: 0 device accessible
1 failed to access device
*************************************************************************/
unsigned char i2c_rep_start(unsigned char address)
{
return i2c_start( address );
}/* i2c_rep_start */
/*************************************************************************
Terminates the data transfer and releases the I2C bus
*************************************************************************/
void i2c_stop(void)
{
/* send stop condition */
TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
// wait until stop condition is executed and bus released
while(TWCR & (1<<TWSTO));
}/* i2c_stop */
/*************************************************************************
Send one byte to I2C device
Input: byte to be transfered
Return: 0 write successful
1 write failed
*************************************************************************/
unsigned char i2c_write( unsigned char data )
{
uint8_t twst;
// send data to the previously addressed device
TWDR = data;
TWCR = (1<<TWINT) | (1<<TWEN);
// wait until transmission completed
while(!(TWCR & (1<<TWINT)));
// check value of TWI Status Register. Mask prescaler bits
twst = TW_STATUS & 0xF8;
if( twst != TW_MT_DATA_ACK) return 1;
return 0;
}/* i2c_write */
/*************************************************************************
Read one byte from the I2C device, request more data from device
Return: byte read from I2C device
*************************************************************************/
unsigned char i2c_readAck(void)
{
TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA);
while(!(TWCR & (1<<TWINT)));
return TWDR;
}/* i2c_readAck */
/*************************************************************************
Read one byte from the I2C device, read is followed by a stop condition
Return: byte read from I2C device
*************************************************************************/
unsigned char i2c_readNak(void)
{
TWCR = (1<<TWINT) | (1<<TWEN);
while(!(TWCR & (1<<TWINT)));
return TWDR;
}/* i2c_readNak */
//Extra a2d stuff: Dont need for i2c, but I want it, so I tossed it in.
// A2D voltage reference select
// *this determines what is used as the
// full-scale voltage point for A2D conversions
#define ADC_REFERENCE_AREF 0x00 ///< 0x00 -> AREF pin, internal VREF turned off
#define ADC_REFERENCE_AVCC 0x01 ///< 0x01 -> AVCC pin, internal VREF turned off
#define ADC_REFERENCE_RSVD 0x02 ///< 0x02 -> Reserved
#define ADC_REFERENCE_256V 0x03 ///< 0x03 -> Internal 2.56V VREF
// default value
#define ADC_REFERENCE ADC_REFERENCE_AVCC
// do not change the mask value
#define ADC_REFERENCE_MASK 0xC0
#define outb(sfr,val) (_SFR_BYTE(sfr) = (val))
#define inb(sfr) _SFR_BYTE(sfr)
// configure A2D converter voltage reference
void a2dSetReference(unsigned char ref)
{
outb(ADMUX, ((inb(ADMUX) & ~ADC_REFERENCE_MASK) | (ref<<6)));
}
//-----end of TWI_Hack.c