26 lines
1.1 KiB
C
26 lines
1.1 KiB
C
#include "header.h"
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#define TWI_PRESCALE_VALUE 1 // can be 1, 4, 16, 64
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#define TWI_FREQ 100000UL // 100kHz I2C
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#define SLAVE_ADDRESS 0x38 // doc AHT20, 7.3 : address of thermistor
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void i2c_init(void) {
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TWSR = TWI_PRESCALE_SET(TWI_PRESCALE_VALUE); // 22.9.3 : (Status Register) set prescaler
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TWBR = ((F_CPU / TWI_FREQ) - 16) / (2 * TWI_PRESCALE_VALUE); // 22.9.1 : (Bit Rate Register) set SCL frequency (formula from datasheet, 22.5.2)
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}
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void i2c_start(void) {
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TWCR = SEND_START_CONDITION; // 22.9.2 : (Control Register) send Start condition (22.7.1) ! writting 1 to TWINT clears it (set it to 0)
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while (!(TEST(TWCR, TWINT))); // p225 example code : Wait for TWINT Flag set. This indicates that the START condition has been transmitted
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uint8_t status = TWSR & 0b11111000; // Table 22-2. Status codes for Master Transmitter Mode
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if (status != TW_START && status != TW_REP_START) {
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TWCR = SEND_STOP_CONDITION;
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return;
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}
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}
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void i2c_stop(void) {
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TWCR = SEND_STOP_CONDITION; // 22.9.2 : send stop condition
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}
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