ATtiny88 datasheet(135/266 Pages) ATMEL

135 / 266 page

135

8008C–AVR–03/09

ATtiny48/88

15.7

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.

r16,TWSR

andi

r16, 0xF8

cpi

r16, START

brne

ERROR

((TWSR & 0xF8) != START)

ERROR();

Check value of TWI Status

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

TWCR to start transmission of

address

wait2:

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.

r16,TWSR

andi

r16, 0xF8

cpi

r16, MT_SLA_ACK

brne

ERROR

((TWSR & 0xF8) !=

MT_SLA_ACK)

ERROR();

Check value of TWI Status

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

wait3:

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.

r16,TWSR

andi

r16, 0xF8

cpi

r16, MT_DATA_ACK

brne

ERROR

((TWSR & 0xF8) !=

MT_DATA_ACK)

ERROR();

Check value of TWI Status

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

Assembly Code Example

C Example

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