220
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 of the bus.
Table 19-3.
Status codes for Master Transmitter 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+W
0
1
X
SLA+W will be transmitted;
ACK or NOT ACK will be received
0x10
A
repeated
START
condition
has
been
transmitted
Load SLA+W
or
Load SLA+R
0
1
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
SLA+W
has
been
transmitted;
ACK has been received
Load
data
byte or
No TWDR ac-
tion or
No TWDR ac-
tion or
No TWDR ac-
tion
0
1
0
1
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
STOP condition followed by a START con-
dition will be transmitted and TWSTO Flag
will be reset
0x20
SLA+W
has
been
transmitted;
NOT ACK has been re-
ceived
Load
data
byte or
No TWDR ac-
tion or
No TWDR ac-
tion or
No TWDR ac-
tion
0
1
0
1
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
STOP condition followed by a START con-
dition will be transmitted and TWSTO Flag
will be reset
0x28
Data byte has been
transmitted;
ACK has been received
Load
data
byte or
No TWDR ac-
tion or
No TWDR ac-
tion or
No TWDR ac-
tion
0
1
0
1
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
STOP condition followed by a START con-
dition will be transmitted and TWSTO Flag
will be reset
0x30
Data byte has been
transmitted;
NOT ACK has been re-
ceived
Load
data
byte or
No TWDR ac-
tion or
No TWDR ac-
tion or
No TWDR ac-
tion
0
1
0
1
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
STOP condition followed by a START con-
dition will be transmitted and TWSTO Flag
will be reset
0x38
Arbitration
lost
in
SLA+W or data bytes
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 entered
A START condition will be transmitted
when the bus becomes free