ATmega640/1280/1281/2560/2561
Assembly Code Example
C Example
Comments
ldi
r16, (1<<TWINT)|(1<<TWSTA)|
TWCR = (1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
1
2
Send START condition
(1<<TWEN)
TWCR, r16
out
wait1:
while (!(TWCR & (1<<TWINT)))
Wait for TWINT Flag set. This
indicates that the START condition
has been transmitted
in
r16,TWCR
;
sbrs r16,TWINT
rjmp wait1
in
andi r16, 0xF8
cpi r16, START
brne ERROR
r16,TWSR
if ((TWSR & 0xF8) != START)
3
Check value of TWI Status
Register. Mask prescaler bits. If
status different from START go to
ERROR
ERROR();
ldi
out
ldi
out
r16, SLA_W
TWDR = SLA_W;
Load SLA_W into TWDR Register.
Clear TWINT bit in TWCR to start
transmission of address
TWDR, r16
TWCR = (1<<TWINT) | (1<<TWEN);
r16, (1<<TWINT) | (1<<TWEN)
TWCR, r16
wait2:
while (!(TWCR & (1<<TWINT)))
4
5
Wait for TWINT Flag set. This
indicates that the SLA+W has been
transmitted, and ACK/NACK has
been received.
in
r16,TWCR
;
sbrs r16,TWINT
rjmp wait2
in
r16,TWSR
if ((TWSR & 0xF8) != MT_SLA_ACK)
Check value of TWI Status
Register. Mask prescaler bits. If
status different from MT_SLA_ACK
go to ERROR
andi r16, 0xF8
ERROR();
cpi
r16, MT_SLA_ACK
brne ERROR
ldi
out
ldi
out
r16, DATA
TWDR = DATA;
Load DATA into TWDR Register.
Clear TWINT bit in TWCR to start
transmission of data
TWDR, r16
TWCR = (1<<TWINT) | (1<<TWEN);
r16, (1<<TWINT) | (1<<TWEN)
TWCR, r16
wait3:
while (!(TWCR & (1<<TWINT)))
6
7
Wait for TWINT Flag set. This
indicates that the DATA has been
transmitted, and ACK/NACK has
been received.
in
r16,TWCR
;
sbrs r16,TWINT
rjmp wait3
in
r16,TWSR
if ((TWSR & 0xF8) != MT_DATA_ACK)
Check value of TWI Status
Register. Mask prescaler bits. If
status different from
andi r16, 0xF8
ERROR();
cpi
r16, MT_DATA_ACK
MT_DATA_ACK go to ERROR
brne ERROR
ldi
out
r16, (1<<TWINT)|(1<<TWEN)|
TWCR = (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO);
Transmit STOP condition
(1<<TWSTO)
TWCR, r16
255
2549A–AVR–03/05
ATMEL [ ATMEL ]
