TWI IC2 Taktrate berechnen

* LM75_Tempsensor.c

* Temperaturmessung (5x pro Sekunde) und Ausgabe der Temperatur als Binärwert am PORTD

* Eine negative Temperatur wird zusätzlich durch eine LED an PB0 angezeigt

* CPU: ATmega88

* FCPU: 8MHz

* I²C CLK Frequency = 100kHz, CLK = 8000000/(16 + 2*(0x50)*1)

*/

#include <avr/io.h>

#include <util/delay.h>

/*** Statusregister codes and other defines ***/

#define START           0x08    // A START condition has been transmitted

#define R_START         0x10    // A REPEATED START condition has been transmitted

#define SLA_W           0xC0    // Slave Address & Write 1100 0000

#define SLA_R           0xC1    // Slave Address & Read 1100 0001

#define MT_SLA_ACK      0x18    // Master Transmit SLA+W has been transmitted & ACK has been received

#define MR_SLA_ACK      0x40    // Master Receive SLA + R has been transmitted & ACK has been received

#define MT_DATA_ACK     0x28    // Master Transmit Data byte has been transmitted & ACK has been received

#define MR_DATA_NACK    0x58    // Master Receive Data byte has been transmitted & NACK has been returned

#define BIT_RATE        0x50    // Set value for the bit rate register TWBR

#define POINTER_ADDRESS 0x00    // LM75 pointer address for temperature register/ Registerwert

void ERROR(void);               // Prototyping of function "ERROR"

/*** Function to send a START Condition ***/

void TWI_START(void)

{

  TWCR = (1<<TWINT)|(1<<TWSTA)|(1<<TWEN);

  // Wait for TWINT Flag set. This indicates that the START condition has been transmitted

  while (!(TWCR & (1<<TWINT)));

  // Check value of TWI statusregister. Mask prescaler bits. If status different from START go to ERROR if ((TWSR & 0xF8) != START)

  ERROR();

}

/*** Function to send the Slave Address with ACK in Master Transmit Mode ***/

void TWI_MT_SLA_ACK(void)

{

  // Load SLA_W into TWDR Register

  TWDR = SLA_W;

  // Clear TWINT bit in TWCR to start transmission of address

  TWCR = (1<<TWINT) | (1<<TWEN);

  // Wait for TWINT Flag set. This indicates that the SLA+W has been transmitted, and ACK/NACK has been received.

  while (!(TWCR & (1<<TWINT)));

  // Check value of TWI status register. Mask prescaler bits. If status different from MT_SLA_ACK go to ERROR

  if ((TWSR & 0xF8) != MT_SLA_ACK)

  ERROR();

}

/*** Function to send 8Bit of data with ACK in Master Transmit Mode **/

void TWI_MT_DATA_ACK(void)

{

  // Load DATA into TWDR register

  TWDR = POINTER_ADDRESS;

  // Clear TWINT bit in TWCR to start transmission of data

  TWCR = (1<<TWINT) | (1<<TWEN);

  // Wait for TWINT flag set. This indicates that the DATA has been transmitted, and ACK/NACK has been received.

  while (!(TWCR & (1<<TWINT)));

  // Check value of TWI status register. Mask prescaler bits. If status different from MT_DATA_ACK go to ERROR

  if ((TWSR & 0xF8) != MT_DATA_ACK)

  ERROR();

}

/*** Function to send a REPEATED START condition **/

void TWI_R_START(void)

{

  // Send a START condition

  TWCR = (1<<TWINT)|(1<<TWSTA)|(1<<TWEN);

  // Wait for TWINT Flag set. This indicates that the START condition has been transmitted

  while (!(TWCR & (1<<TWINT)));

  // Check value of TWI statusregister. Mask prescaler bits. If status different from R_START go to ER-ROR

  if ((TWSR & 0xF8) != R_START)

  ERROR();

}

/*** Function to send the Slave Address in Master Receive Mode with Acknowledge **/

void TWI_MR_SLA_ACK(void)

{

  // Load SLA_R into TWDR Register

  TWDR = SLA_R;

  // Clear TWINT bit in TWCR to start transmission of address

  TWCR = (1<<TWINT) | (1<<TWEN);

  // Wait for TWINT Flag set. This indicates that the SLA+W has been transmitted, and ACK/NACK has been received.

  while (!(TWCR & (1<<TWINT)));

  // Check value of TWI status register. Mask prescaler bits. If status different from MR_SLA_ACK go to ERROR

  if ((TWSR & 0xF8) != MR_SLA_ACK)

  ERROR();

}

/*** Function to read one Databyte in Master Receive Mode with NACK ***/

uint8_t TWI_READ_DATABYTE_NACK(void)

{

  // Read one data byte

  TWCR = (1<<TWINT)| (1<<TWEN);

  // Wait for TWINT flag set. This indicates that the DATA has been transmitted, and ACK/NACK has been received.

  while (!(TWCR & (1<<TWINT)));

  // Check value of TWI status register. Mask prescaler bits. If status different from MR_DATA_NACK go to ERROR

  if ((TWSR & 0xF8) != MR_DATA_NACK)

  ERROR();

  return TWDR; // Return the value of data register

}

/*** function to send a STOP condition ***/

void TWI_STOP(void)

{

  TWCR = (1<<TWINT)|(1<<TWEN)|(1<<TWSTO); // Transmit STOP condition

}

/*** function to show a bus error ***/

void ERROR(void)

{

  PORTB |= (1<<PB1); // ERROR LED ON

}

uint8_t LSByte, MSByte;

uint16_t data_16bit, temperature, high_byte, low_byte;

int main(void)

{

  DDRD = 0xFF;        // PORTD = output

  DDRC = 0x3F;        // PC0 ... PC5 = output

  DDRB = 0x03;        // PB0 and PB1 = output

  TWBR = BIT_RATE;    // Set the TWI clock-frequency in bit rate register

  while(1)

  {

    TWI_START();                        // Send START condition

    TWI_MT_SLA_ACK();                   // Master Transmit Slave Address with ACK

    TWI_MT_DATA_ACK();                  // Master Transmit Data with ACK

    TWI_STOP();                         // Send STOP condition

    _delay_ms(200);                     // wait 200ms for new readout

  }

}

definieren im Quelltextkopf :

......

#define  F_CPU 16000000UL  // 16MHz Q-frequenz

#define  SCL_CLOCK 100000UL // 100kHz TWI Clock

......

*

*

*

void i2c_init()

{

  /* 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 */