ATMEGA48V_06 Datasheet, PDF (224/374 Pages) ATMEL Corporation – 8-bit Microcontroller with 8K Bytes In-System Programmable Flash

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 20-2.
Status Code
(TWSR)
Prescaler Bits
are 0
0x08
0x10
Status codes for Master Transmitter Mode
Status of the 2-wire Serial Bus
and 2-wire Serial Interface
Hardware
A START condition has been
transmitted
A repeated START condition
has been transmitted
Application Software Response
To/from TWDR
To TWCR
STA STO TWIN
T
Load SLA+W
0
0
1
Load SLA+W or
Load SLA+R
0
0
1
0
0
1
0x18
SLA+W has been transmitted; Load data byte or
0
0
1
ACK has been received
No TWDR action or
1
0
1
No TWDR action or
0
1
1
No TWDR action
1
1
1
0x20
SLA+W has been transmitted; Load data byte or
0
0
1
NOT ACK has been received
No TWDR action or
1
0
1
No TWDR action or
0
1
1
No TWDR action
1
1
1
0x28
Data byte has been transmit- Load data byte or
0
0
1
ted;
ACK has been received
No TWDR action or
1
0
1
No TWDR action or
0
1
1
No TWDR action
1
1
1
0x30
Data byte has been transmit- Load data byte or
0
0
1
ted;
NOT ACK has been received
No TWDR action or
1
0
1
No TWDR action or
0
1
1
No TWDR action
1
1
1
0x38
Arbitration lost in SLA+W or No TWDR action or
0
0
1
data bytes
No TWDR action
1
0
1
TWE
A
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Next Action Taken by TWI Hardware
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+R will be transmitted;
Logic will switch to Master Receiver mode
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
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
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
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
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
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
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
STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
2-wire Serial Bus will be released and not addressed
Slave mode entered
A START condition will be transmitted when the bus
becomes free
224 ATmega48/88/168
2545J–AVR–12/06