Datasheet

214
2490R–AVR–02/2013
ATmega64(L)
This scheme is repeated until the last byte has been sent and the transfer is ended by generat-
ing a STOP condition or a repeated START condition. A STOP condition is generated by writing
the following value to TWCR:
A REPEATED START condition is generated by writing the following value to TWCR:
After a repeated START condition (state 0x10) the Two-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 without losing control of the bus.
TWCR TWINT TWEA TWSTA TWSTO TWWC TWEN – TWIE
Value 1
X01X10 X
TWCR TWINT
TWEA TWSTA TWSTO TWWC TWEN – TWIE
Value 1
X10X10 X
Table 88. Status Codes for Master Transmitter Mode
Status Code
(TWSR)
Prescaler Bits
are 0
Status of the Two-wire Serial
Bus and Two-wire Serial Inter-
face Hardware
Application Software Response
Next Action Taken by TWI Hardware
To/from TWDR
To TWCR
STA STO TWINT TWEA
0x08 A START condition has been
transmitted
Load SLA+W 0 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
0
0
0
1
1
X
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 action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
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 condition will be
transmitted and TWSTO flag will be reset
0x20 SLA+W has been transmitted;
NOT ACK has been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
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 condition will be
transmitted and TWSTO flag will be reset
0x28 Data byte has been transmit-
ted;
ACK has been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
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 condition will be
transmitted and TWSTO flag will be reset
0x30 Data byte has been transmit-
ted;
NOT ACK has been received
Load data byte or
No TWDR action or
No TWDR action or
No TWDR action
0
1
0
1
0
0
1
1
1
1
1
1
X
X
X
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 condition will be
transmitted and TWSTO flag will be reset
0x38 Arbitration lost in SLA+W or
data bytes
No TWDR action or
No TWDR action
0
1
0
0
1
1
X
X
Two-wire Serial Bus will be released and not ad-
dressed slave mode entered
A START condition will be transmitted when the bus
becomes free