ATMEGA8_08 Datasheet, PDF (183/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

ATmega8(L)
enables the Master to switch between Slaves, Master Transmitter mode and Master Receiver
mode without losing control over the bus.
Table 67. Status codes for Master Receiver Mode
Status Code
(TWSR)
Prescaler Bits
are 0
0x08
0x10
Status of the Two-wire Serial
Bus and Two-wire Serial Inter-
face Hardware
A START condition has been
transmitted
A repeated START condition
has been transmitted
Application Software Response
To/from TWDR
To TWCR
STA STO TWINT
Load SLA+R
0
0
1
Load SLA+R or
Load SLA+W
0
0
1
0
0
1
0x38
Arbitration lost in SLA+R or NOT No TWDR action or
0
0
1
ACK bit
No TWDR action
1
0
1
0x40
SLA+R has been transmitted; No TWDR action or
0
0
1
ACK has been received
No TWDR action
0
0
1
TWEA
X
X
X
X
X
0
1
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
Two-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
0x48
0x50
0x58
SLA+R has been transmitted; No TWDR action or
1
0
1
X Repeated START will be transmitted
NOT ACK has been received No TWDR action or
0
1
1
X STOP condition will be transmitted and TWSTO Flag will
be reset
No TWDR action
1
1
1
X STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
Data byte has been received; Read data byte or
0
0
1
0 Data byte will be received and NOT ACK will be
ACK has been returned
returned
Read data byte
0
0
1
1 Data byte will be received and ACK will be returned
Data byte has been received; Read data byte or
1
0
1
X Repeated START will be transmitted
NOT ACK has been returned
Read data byte or
0
1
1
X STOP condition will be transmitted and TWSTO Flag will
be reset
Read data byte
1
1
1
X STOP condition followed by a START condition will be
transmitted and TWSTO Flag will be reset
2486T–AVR–05/08
183