Datasheet

191
ATmega48PA/88PA/168PA [DATASHEET]
9223F–AVR–04/14
Table 22-2. Assembly Code Examples
Assembly Code Example C Example Comments
1
ldi r16,
(1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
out TWCR, r16
TWCR =
(1<<TWINT)|(1<<TWSTA)|
(1<<TWEN)
Send START condition
2
wait1:
in 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
3
in r16,TWSR
andi r16, 0xF8
cpi r16, START
brne ERROR
if ((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
4
wait2:
in 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.
5
in r16,TWSR
andi r16, 0xF8
cpi r16, MT_SLA_ACK
brne ERROR
if ((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
6
wait3:
in 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.
7
in r16,TWSR
andi r16, 0xF8
cpi r16, MT_DATA_ACK
brne ERROR
if ((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