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191
8154B–AVR–07/09
ATmega16A
Table 20-3.
Status Codes for Master Receiver 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
$08
A START condition has been
transmitted
Load SLA+R
0
1
X
SLA+R will be transmitted
ACK or NOT ACK will be received
$10
A repeated START condition
has been transmitted
Load SLA+R or
Load SLA+W
0
1
X
SLA+R will be transmitted
ACK or NOT ACK will be received
SLA+W will be transmitted
Logic will switch to masTer Transmitter mode
$38
Arbitration lost in SLA+R or NOT
ACK bit
No TWDR action or
No TWDR action
0
1
0
1
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
$40
SLA+R has been transmitted;
ACK has been received
No TWDR action or
No TWDR action
0
1
0
1
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
$48
SLA+R has been transmitted;
NOT ACK has been received
No TWDR action or
No TWDR action
1
0
1
0
1
X
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
$50
Data byte has been received;
ACK has been returned
Read data byte or
Read data byte
0
1
0
1
Data byte will be received and NOT ACK will be
returned
Data byte will be received and ACK will be returned
$58
Data byte has been received;
NOT ACK has been returned
Read data byte or
Read data byte
1
0
1
0
1
X
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