223
7530J–AVR–03/12
Atmel ATmega48/88/168 Automotive
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 over the bus.
Table 19-4.
Status codes for Master Receiver Mode
Status
Code
(TWSR)
Prescaler
Bits
are 0
Status of the 2-wire Se-
rial Bus and 2-wire Seri-
al Interface Hardware
Application Software Response
Next Action Taken by TWI Hardware
To/from
TWDR
To TWCR
ST
A
ST
O
TWI
NT
TW
EA
0x08
A START condition has
been transmitted
Load SLA+R
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
1
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 ac-
tion or
No TWDR ac-
tion
0
1
0
1
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 trans-
mitted;
ACK has been received
No TWDR ac-
tion or
No TWDR ac-
tion
0
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 trans-
mitted;
NOT ACK has been re-
ceived
No TWDR ac-
tion or
No TWDR ac-
tion or
No TWDR ac-
tion
1
0
1
0
1
X
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
STOP condition followed by a START con-
dition will be transmitted and TWSTO Flag
will be reset
0x50
Data byte has been re-
ceived;
ACK has been returned
Read
data
byte or
Read
data
byte
0
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 re-
ceived;
NOT ACK has been re-
turned
Read
data
byte or
Read
data
byte or
Read
data
byte
1
0
1
0
1
X
Repeated START will be transmitted
STOP condition will be transmitted and
TWSTO Flag will be reset
STOP condition followed by a START con-
dition will be transmitted and TWSTO Flag
will be reset