Atmega128(l) – Rainbow Electronics ATmega128L User Manual
Page 203
203
ATmega128(L)
2467B–09/01
Note:
For I/O registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”, and “SBI” instructions must be replaced with
instructions that allow access to extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and “CBR”.
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 address
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