Datasheet

Assembly Code Example C Example Comments
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.
7
in r16,TWSR0
andi r16, 0xF8
cpi r16, MT_DATA_ACK
brne ERROR
if ((TWSR0 & 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 TWCR0, r16
TWCR0 = (1<<TWINT)|
(1<<TWEN)|(1<<TWSTO);
Transmit STOP condition.
26.7 Transmission Modes
The TWI can operate in one of four major modes:
• Master Transmitter (MT)
• Master Receiver (MR)
• Slave Transmitter (ST)
• Slave Receiver (SR)
Several of these modes can be used in the same application. As an example, the TWI can use MT mode
to write data into a TWI EEPROM, MR mode to read the data back from the EEPROM. If other masters
are present in the system, some of these might transmit data to the TWI, and then SR mode would be
used. It is the application software that decides which modes are legal.
The following sections describe each of these modes. Possible status codes are described along with
figures detailing data transmission in each of the modes. These figures use the following abbreviations:
S START condition
Rs REPEATED START condition
R Read bit (high level at SDA)
ATmega48PA/88PA/168PA
Two-Wire Serial Interface (TWI)
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40002011A-page 282