AT90SCR100 datasheet(307/433 Pages) ATMEL

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307

TPR0327AY–SMS–30Jan09

AT90SCR100

• When the TWINT Flag is set, the user must update all TWI Registers with the value relevant

for the next TWI bus cycle. As an example, TWDR must be loaded with the value to be

transmitted in the next bus cycle.

• After all TWI Register updates and other pending application software tasks have been

completed, TWCR is written. When writing TWCR, the TWINT bit should be set. Writing a

one to TWINT clears the flag. The TWI will then start executing whatever operation was

specified by the TWCR setting.

In the following an assembly and C implementation of the example is given. Note that the code

below assumes that several definitions have been made, for example by using include-files.

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

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

AT90SCR100 Datasheet(PDF) 307 Page - ATMEL Corporation

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