Datasheet

227
2545T–AVR–05/11
ATmega48/88/168
the Master to switch between Slaves, Master Transmitter mode and Master Receiver mode with-
out losing control over the bus.
Table 22-3. Status codes for master receiver mode.
Status code
(TWSR)
prescaler bits
are 0
Status of the 2-wire serial bus
and 2-wire serial interface
hardware
Application software response
Next action taken by TWI hardware
To/from TWDR
To TWCR
STA STO TWIN
T
TWE
A
0x08 A START condition has been
transmitted
Load SLA+R 0 0 1 X SLA+R will be transmitted
ACK or NOT ACK will be received
0x10 A repeated START condition
has been transmitted
Load SLA+R or
load SLA+W
0
0
0
0
1
1
X
X
SLA+R will be transmitted
ACK or NOT ACK will be received
SLA+W will be transmitted
Logic will switch to master transmitter mode
0x38 Arbitration lost in SLA+R or
NOT ACK bit
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 will be entered
A START condition will be transmitted when the bus
becomes free
0x40 SLA+R has been transmitted;
ACK has been received
No TWDR action or
no TWDR action
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
0x48 SLA+R has been transmitted;
NOT ACK has been received
No TWDR action or
no TWDR action or
no TWDR action
1
0
1
0
1
1
1
1
1
X
X
X
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
0x50 Data byte has been received;
ACK has been returned
Read data byte or
read data byte
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
0x58 Data byte has been received;
NOT ACK has been returned
Read data byte or
read data byte or
read data byte
1
0
1
0
1
1
1
1
1
X
X
X
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