Datasheet

TWINT clears the flag. The TWI n will then commence executing whatever operation was specified
by the TWCRn setting.
The following table lists assembly and C implementation examples for TWI0. Note that the code below
assumes that several definitions have been made, e.g. by using include-files.
Table 23-2. Assembly and C Code Example
Assembly Code Example C Example Comments
1
ldi r16, (1<<TWINT)|
(1<<TWSTA)|(1<<TWEN)
out TWCR0, r16
TWCR0 = (1<<TWINT)|
(1<<TWSTA)|(1<<TWEN)
Send START condition
2
wait1:
in r16,TWCR0
sbrs r16,TWINT
rjmp wait1
while (!(TWCR0 &
(1<<TWINT)));
Wait for TWINT Flag set. This indicates
that the START condition has been
transmitted.
3
in r16,TWSR0
andi r16, 0xF8
cpi r16, START
brne ERROR
if ((TWSR0 & 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 TWDR0, r16
ldi r16, (1<<TWINT) |
(1<<TWEN)
out TWCR0, r16
TWDR0 = SLA_W;
TWCR0 = (1<<TWINT) |
(1<<TWEN);
Load SLA_W into TWDR Register. Clear
TWINT bit in TWCR to start transmission of
address.
4
wait2:
in r16,TWCR0
sbrs r16,TWINT
rjmp wait2
while (!(TWCR0 &
(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,TWSR0
andi r16, 0xF8
cpi r16, MT_SLA_ACK
brne ERROR
if ((TWSR0 & 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 TWDR0, r16
ldi r16, (1<<TWINT) |
(1<<TWEN)
out TWCR, r16
TWDR0 = DATA;
TWCR0 = (1<<TWINT) |
(1<<TWEN);
Load DATA into TWDR Register. Clear
TWINT bit in TWCR to start transmission of
data.
6
wait3:
in r16,TWCR0
sbrs r16,TWINT
rjmp wait3
while (!(TWCR0 &
(1<<TWINT)));
Wait for TWINT Flag set. This indicates
that the DATA has been transmitted, and
ACK/NACK has been received.
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
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