Atmel ATmega48PV Manual page 232

Table 19-3. Status codes for Master Receiver Mode
Status Code
(TWSR) Status of the 2-wire Serial Bus
Prescaler Bits and 2-wire Serial Interface
are 0 Hardware
0x08 A START condition has been
transmitted
0x10 A repeated START condition
has been transmitted
0x38 Arbitration lost in SLA+R or
NOT ACK bit
0x40 SLA+R has been transmitted;
ACK has been received
0x48 SLA+R has been transmitted;
NOT ACK has been received
0x50 Data byte has been received;
ACK has been returned
0x58 Data byte has been received;
NOT ACK has been returned
8025I–AVR–02/09
the Master to switch between Slaves, Master Transmitter mode and Master Receiver mode with-
out losing control over the bus.
Application Software Response
To/from TWDR
Load SLA+R
Load SLA+R or
Load SLA+W
No TWDR action or
No TWDR action
No TWDR action or
No TWDR action
No TWDR action or
No TWDR action or
No TWDR action
Read data byte or
Read data byte
Read data byte or
Read data byte or
Read data byte
ATmega48P/88P/168P/328P
To TWCR
STA STO TWIN TWE
T A
0 0 1 X
0 0 1 X
0 0 1 X
0 0 1 X
1 0 1 X
0 0 1 0
0 0 1 1
1 0 1 X
0 1 1 X
1 1 1 X
0 0 1 0
0 0 1 1
1 0 1 X
0 1 1 X
1 1 1 X
Next Action Taken by TWI Hardware
SLA+R will be transmitted
ACK or NOT ACK will be received
SLA+R will be transmitted
ACK or NOT ACK will be received
SLA+W will be transmitted
Logic will switch to Master Transmitter mode
2-wire Serial Bus will be released and not addressed
Slave mode will be entered
A START condition will be transmitted when the bus
becomes free
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
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 received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
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
232