Table 75. Status Codes for Master Receiver Mode
Status Code
(TWSR)
Prescaler Bits
are 0
Application Software Response
To TWCR
STO TWINT
Status of the Two-wire Serial
Bus and Two-wire Serial Inter-
face Hardware
To/from TWDR
STA
0
TWEA
X
Next Action Taken by TWI Hardware
$08
A START condition has been Load SLA+R
transmitted
0
1
SLA+R will be transmitted
ACK or NOT ACK will be received
$10
A
repeated START condition Load SLA+R or
0
0
0
0
1
1
X
X
SLA+R will be transmitted
ACK or NOT ACK will be received
SLA+W will be transmitted
has been transmitted
Load SLA+W
Logic will switch to masTer Transmitter mode
$38
$40
$48
Arbitration lost in SLA+R or NOT No TWDR action or
0
1
0
0
1
1
X
X
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
ACK bit
No TWDR action
SLA+R has been transmitted;
ACK has been received
No TWDR action or
No TWDR action
0
0
0
0
1
1
0
1
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
SLA+R has been transmitted;
NOT ACK has been received
No TWDR action or
No TWDR action or
1
0
0
1
1
1
X
X
Repeated START will be transmitted
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
$50
$58
Data byte has been received;
ACK has been returned
Read data byte or
Read data byte
0
0
0
1
0
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
0
1
1
Data byte has been received;
NOT ACK has been returned
Read data byte or
Read data byte or
1
0
0
1
1
1
X
X
Repeated START will be transmitted
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
188
ATmega32(L)
2503J–AVR–10/06
ATMEL [ ATMEL ]
