MEGA128CAN Datasheet, PDF (216/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

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.
Table 90. Status Codes for Master Transmitter 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
Load SLA+W
X
0
Load SLA+W or
X
0
Load SLA+R
X
0
0x18
SLA+W has been transmitted; Load data byte or 0
0
ACK has been received
No TWDR action or 1
0
No TWDR action or 0
1
No TWDR action
1
1
0x20
SLA+W has been transmitted; Load data byte or 0
0
NOT ACK has been received
No TWDR action or 1
0
No TWDR action or 0
1
No TWDR action
1
1
0x28
Data byte has been transmitted; Load data byte or 0
0
ACK has been received
No TWDR action or 1
0
No TWDR action or 0
1
No TWDR action
1
1
0x30
Data byte has been transmitted; Load data byte or 0
0
NOT ACK has been received
No TWDR action or 1
0
No TWDR action or 0
1
No TWDR action
1
1
0x38
Arbitration lost in SLA+W or data No TWDR action or 0
0
bytes
No TWDR action
1
0
TWINT
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
TWEA
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Next Action Taken by TWI Hardware
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+W will be transmitted;
ACK or NOT ACK will be received
SLA+R will be transmitted;
Logic will switch to master receiver mode
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
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
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
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
Two-wire Serial Bus will be released and not addressed
slave mode entered
A START condition will be transmitted when the bus be-
comes free
216 AT90CAN128
4250E–CAN–12/04