ATmega128 datasheet(212/386 Pages) ATMEL

212 / 386 page

212

2467S–AVR–07/09

ATmega128

Note:

For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with

instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.

Assembly Code Example

C Example

Comments

ldi

r16,

(1<<TWINT)|(1<<TWSTA)|

(1<<TWEN)

out

TWCR, r16

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

(1<<TWEN)

Send START condition

wait1:

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

r16,TWSR

andi

r16, 0xF8

cpi

r16, START

brne

ERROR

((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

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 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

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 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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