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ATmega32A Datasheet(PDF) 186 Page - ATMEL Corporation |
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ATmega32A Datasheet(HTML) 186 Page - ATMEL Corporation |
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186 / 352 page  186 8155B–AVR–07/09 ATmega32A 20.7 Transmission Modes The TWI can operate in one of four major modes. These are named Master Transmitter (MT), Master Receiver (MR), Slave Transmitter (ST) and Slave Receiver (SR). Several of these modes can be used in the same application. As an example, the TWI can use MT mode to write data into a TWI EEPROM, MR mode to read the data back from the EEPROM. If other masters are present in the system, some of these might transmit data to the TWI, and then SR mode would be used. It is the application software that decides which modes are legal. Assembly code example C example Comments 1 ldi r16, (1<<TWINT)|(1<<TWSTA)| (1<<TWEN) out TWCR, r16 TWCR = (1<<TWINT)|(1<<TWSTA)| (1<<TWEN) Send START condition 2 wait1: in r16,TWCR sbrs r16,TWINT rjmp wait1 while (!(TWCR & (1<<TWINT))) ; Wait for TWINT Flag set. This indicates that the START condition has been transmitted 3 in r16,TWSR andi r16, 0xF8 cpi r16, START brne ERROR if ((TWSR & 0xF8) != START) ERROR(); Check value of TWI Status Register. Mask prescaler bits. If status different from START go to ERROR ldi r16, SLA_W out TWDR, r16 ldi r16, (1<<TWINT) | (1<<TWEN) out TWCR, r16 TWDR = SLA_W; TWCR = (1<<TWINT) | (1<<TWEN); Load SLA_W into TWDR Register. Clear TWINT bit in TWCR to start transmission of address 4 wait2: in r16,TWCR sbrs r16,TWINT rjmp wait2 while (!(TWCR & (1<<TWINT))) ; Wait for TWINT Flag set. This indicates that the SLA+W has been transmitted, and ACK/NACK has been received. 5 in r16,TWSR andi r16, 0xF8 cpi r16, MT_SLA_ACK brne ERROR if ((TWSR & 0xF8) != MT_SLA_ACK) ERROR(); Check value of TWI Status Register. Mask prescaler bits. If status different from MT_SLA_ACK go to ERROR ldi r16, DATA out TWDR, r16 ldi r16, (1<<TWINT) | (1<<TWEN) out TWCR, r16 TWDR = DATA; TWCR = (1<<TWINT) | (1<<TWEN); Load DATA into TWDR Register. Clear TWINT bit in TWCR to start transmission of data 6 wait3: in r16,TWCR sbrs r16,TWINT rjmp wait3 while (!(TWCR & (1<<TWINT))) ; Wait for TWINT Flag set. This indicates that the DATA has been transmitted, and ACK/NACK has been received. 7 in r16,TWSR andi r16, 0xF8 cpi r16, MT_DATA_ACK brne ERROR if ((TWSR & 0xF8) != MT_DATA_ACK) ERROR(); Check value of TWI Status Register. Mask prescaler bits. If status different from MT_DATA_ACK go to ERROR ldi r16, (1<<TWINT)|(1<<TWEN)| (1<<TWSTO) out TWCR, r16 TWCR = (1<<TWINT)|(1<<TWEN)| (1<<TWSTO); Transmit STOP condition |
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