Assembly Code Example
C Example
TWCR = (1<<TWINT)|(1<<TWSTA)|
Comments
ldi r16, (1<<TWINT)|(1<<TWSTA)|
1
2
Send START condition
(1<<TWEN)
out TWCR, r16
wait1:
(1<<TWEN)
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
r16,TWSR
if ((TWSR & 0xF8) != START)
3
Check value of TWI Status
Register. Mask prescaler bits. If
status different from START go to
ERROR
andi r16, 0xF8
cpi r16, START
brne ERROR
ERROR();
ldi r16, SLA_W
out TWDR, r16
ldi r16, (1<<TWINT) | (1<<TWEN)
out TWCR, r16
wait2:
TWDR = SLA_W;
Load SLA_W into TWDR Register.
Clear TWINT bit in TWCR to start
transmission of address
TWCR = (1<<TWINT) | (1<<TWEN);
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 r16, DATA
TWDR = DATA;
Load DATA into TWDR Register.
Clear TWINT bit in TWCR to start
transmission of data
out TWDR, r16
TWCR = (1<<TWINT) | (1<<TWEN);
ldi r16, (1<<TWINT) | (1<<TWEN)
out 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
brne ERROR
MT_DATA_ACK go to ERROR
ldi r16, (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO)
TWCR = (1<<TWINT)|(1<<TWEN)|
(1<<TWSTO);
Transmit STOP condition
out TWCR, r16
174
ATmega8(L)
2486M–AVR–12/03
ATMEL [ ATMEL ]
