Atmel ATmega128 User Manual

212
2467S–AVR–07/09
ATmega128
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 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

Atmel ATmega128 Specifications

General

Brand	Atmel
Model	ATmega128
Category	Microcontrollers
Language	English