ATmega48PA/88PA/168PA/328P
After a repeated START condition (state 0x10) the 2-wire Serial Interface can access the same
Slave again, or a new Slave without transmitting a STOP condition. Repeated START enables
the Master to switch between Slaves, Master Transmitter mode and Master Receiver mode with-
out losing control of the bus.
Table 21-2. Status codes for Master Transmitter Mode
Status Code
(TWSR)
Prescaler Bits
are 0
Application Software Response
To/from TWDR To TWCR
STO TWIN
Status of the 2-wire Serial Bus
and 2-wire Serial Interface
Hardware
STA
0
TWE
A
Next Action Taken by TWI Hardware
T
0x08
0x10
A START condition has been
transmitted
Load SLA+W
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
A repeated START condition
has been transmitted
Load SLA+W or
Load SLA+R
0
0
0
0
1
1
X
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+R will be transmitted;
Logic will switch to Master Receiver mode
0x18
0x20
0x28
0x30
0x38
SLA+W has been transmitted;
ACK has been received
Load data byte or
0
0
1
X
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
Load data byte or
1
0
1
0
1
1
X
X
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
SLA+W has been transmitted;
NOT ACK has been received
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
Load data byte or
1
0
1
0
1
1
X
X
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte has been transmit-
ted;
ACK has been received
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
Load data byte or
1
0
1
0
1
1
X
X
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte has been transmit-
ted;
NOT ACK has been received
Data byte will be transmitted and ACK or NOT ACK will
be received
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
No TWDR action
1
1
1
X
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Arbitration lost in SLA+W or
data bytes
No TWDR action or
No TWDR action
0
1
0
0
1
1
X
X
2-wire Serial Bus will be released and not addressed
Slave mode entered
A START condition will be transmitted when the bus
becomes free
229
8161D–AVR–10/09
ATMEL [ ATMEL ]
