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7679H–CAN–08/08
AT90CAN32/64/128
18.8.3 Slave Receiver Mode
In the Slave Receiver mode, a number of data bytes are received from a master transmitter (see
Figure 18-15). All the status codes mentioned in this section assume that the prescaler bits are
zero or are masked to zero.
Figure 18-15. Data Transfer in Slave Receiver Mode
Table 18-4. Status Codes for Master Receiver Mode
Status Code
(TWSR)
Prescaler Bits
are 0
Status of the Two-wire Serial Bus
and Two-wire Serial Interface
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+R X 0 1 X SLA+R will be transmitted
ACK or NOT ACK will be received
0x10 A repeated START condition has
been transmitted
Load SLA+R or
Load SLA+W
X
X
0
0
1
1
X
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
0x38 Arbitration lost in SLA+R or NOT
ACK bit
No TWDR action or
No TWDR action
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
0x40 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
0x48 SLA+R has been transmitted;
NOT ACK has been received
No TWDR action or
No TWDR action or
No TWDR action
1
0
1
0
1
1
1
1
1
X
X
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
0x50 Data byte has been received;
ACK has been returned
Read data byte or
Read data byte
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
0x58 Data byte has been received;
NOT ACK has been returned
Read data byte or
Read data byte or
Read data byte
1
0
1
0
1
1
1
1
1
X
X
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
Device 1
Device 2
Device 3
Device n
SDA
SCL
........
R1 R2
V
CC
MASTER
SLAVE
TRANSMITTER
RECEIVER
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