ATmega8(L)
In all sleep modes other than Idle mode, the clock system to the TWI is turned off. If the TWEA
bit is set, the interface can still acknowledge its own slave address or the general call address by
using the Two-wire Serial Bus clock as a clock source. The part will then wake up from sleep
and the TWI will hold the SCL clock will low during the wake up and until the TWINT Flag is
cleared (by writing it to one). Further data transmission will be carried out as normal, with the
AVR clocks running as normal. Observe that if the AVR is set up with a long start-up time, the
SCL line may be held low for a long time, blocking other data transmissions.
Note that the Two-wire Serial Interface Data Register – TWDR does not reflect the last byte
present on the bus when waking up from these sleep modes.
Table 69. Status Codes for Slave Transmitter Mode
Status Code
(TWSR)
Prescaler Bits
are 0
Application Software Response
Status of the Two-wire Serial Bus
and Two-wire Serial Interface
Hardware
To TWCR
To/from TWDR
Load data byte or
Load data byte
STA
X
STO
0
TWINT
1
TWEA
0
Next Action Taken by TWI Hardware
0xA8
0xB0
0xB8
0xC0
Own SLA+R has been received;
ACK has been returned
Last data byte will be transmitted and NOT ACK should
be received
X
0
1
1
Data byte will be transmitted and ACK should be re-
ceived
Arbitration lost in SLA+R/W as Load data byte or
Master; own SLA+R has been
X
X
0
0
1
1
0
1
Last data byte will be transmitted and NOT ACK should
be received
Data byte will be transmitted and ACK should be re-
ceived
received; ACK has been returned
Load data byte
Data byte in TWDR has been
transmitted; ACK has been
received
Load data byte or
Load data byte
X
X
0
0
1
1
0
1
Last data byte will be transmitted and NOT ACK should
be received
Data byte will be transmitted and ACK should be re-
ceived
Data byte in TWDR has been
transmitted; NOT ACK has been
received
No TWDR action or
No TWDR action or
0
0
0
0
1
1
0
1
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
No TWDR action or
No TWDR action
1
1
0
0
1
1
0
1
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
0xC8
Last data byte in TWDR has been No TWDR action or
0
0
0
0
1
1
0
1
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”
Switched to the not addressed Slave mode;
no recognition of own SLA or GCA;
a START condition will be transmitted when the bus
becomes free
transmitted (TWEA
has been received
= “0”); ACK
No TWDR action or
No TWDR action or
1
1
0
0
1
1
0
1
No TWDR action
Switched to the not addressed Slave mode;
own SLA will be recognized;
GCA will be recognized if TWGCE = “1”;
a START condition will be transmitted when the bus
becomes free
189
2486T–AVR–05/08
ATMEL [ ATMEL ]
