Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 222
21.7 Transmission modes
The TWI can operate in one of four major modes. These are named Master Transmitter (MT), Master Receiver
(MR), Slave Transmitter (ST) and 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 contain the following abbreviations:
S:START condition
Rs:REPEATED START condition
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
Table 21-2. Assembly code and C code examples
Assembly code example C example Comments