Datasheet

Assembly Code Example C Example Comments
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.
23.7. 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)
W Write bit (low level at SDA)
A Acknowledge bit (low level at SDA)
A Not acknowledge bit (high level at SDA)
Data 8-bit data byte
P STOP condition
SLA Slave Address
Circles are used to indicate that the TWINT Flag is set. The numbers in the circles show the status code
held in TWSRn, with the prescaler bits masked to zero. At these points, actions must be taken by the
application to continue or complete the TWI transfer. The TWI transfer is suspended until the TWINT Flag
is cleared by software.
When the TWINT Flag is set, the status code in TWSRn is used to determine the appropriate software
action. For each status code, the required software action and details of the following serial transfer are
given below in the Status Code table for each mode. Note that the prescaler bits are masked to zero in
these tables.
Atmel ATmega644A [DATASHEET]
Atmel-42716C-ATmega644A_Datasheet_Complete-10/2016
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