Datasheet

The following table lists assembly and C implementation examples. Note that the code below assumes
that several definitions have been made, e.g. by using include-files.
Table 25-2. Assembly and C Code Example
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.
25.6.1 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.
AVR 8-Bit Microcontroller
TWI - Two-wire Serial Interface
© 2017 Microchip Technology Inc.
Datasheet Complete
40001974A-page 224