ATmega16A datasheet(185/352 Pages) ATMEL

185 / 352 page

185

8154B–AVR–07/09

ATmega16A

• 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 commence 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 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

ATmega16A Datasheet(PDF) 185 Page - ATMEL Corporation

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