Rainbow Electronics ATmega128L - Manual (Page 206)

206
ATmega128(L)
2467B–09/01
After a repeated START condition (state $10) the 2-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 87. Status Codes for Master Transmitter Mode
Status Code
(TWSR)
Prescaler Bits
are 0
Status of the 2-wire Serial Bus
and 2-wire Serial Interface Hard-
ware
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+W X 0 1 X SLA+W will be transmitted;
ACK or NOT ACK will be received
$10 A repeated START condition
has been transmitted Load SLA+W or
Load SLA+R
X
X
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
$18 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
$20 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
$28 Data byte 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
$30 Data byte 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
$38 Arbitration lost in SLA+W or data
bytes No TWDR action or
No TWDR action
0
1
0
0
1
1
X
X
2-wire Serial Bus will be released and not addressed
slave mode entered
A START condition will be transmitted when the bus be-
comes free