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32059L–AVR32–01/2012
AT32UC3B
19.10.6
Master Receiver Mode
The read sequence begins by setting the START bit. After the start condition has been sent, the
master sends a 7-bit slave address to notify the slave device. The bit following the slave address
indicates the transfer direction, 1 in this case (MREAD = 1 in MMR). During the acknowledge
clock pulse (9th pulse), the master releases the data line (HIGH), enabling the slave to pull it
down in order to generate the acknowledge. The master polls the data line during this clock
pulse and sets the NACK bit in the status register if the slave does not acknowledge the byte.
If an acknowledge is received, the master is then ready to receive data from the slave. After data
has been received, the master sends an acknowledge condition to notify the slave that the data
has been received except for the last data, after the stop condition. See
Figure 19-9. When the
RXRDY bit is set in the status register, a character has been received in the receive-holding reg-
ister (RHR). The RXRDY bit is reset when reading the RHR.
When a single data byte read is performed, with or without internal address (IADR), the START
and STOP bits must be set at the same time. See
Figure 19-9. When a multiple data byte read is
performed, with or without IADR, the STOP bit must be set after the next-to-last data received.
Figure 19-9. Master Read with One Data Byte
Figure 19-10. Master Read with Multiple Data Bytes
RXRDY is used as Receive Ready for the Peripheral DMA Controller receive channel.
19.10.7
Internal Address
The TWI interface can perform various transfer formats: Transfers with 7-bit slave address
devices and 10-bit slave address devices.
A
S
DADR
R
DATA
N
P
TXCOMP
Write START &
STOP Bit
RXRDY
Read RHR
TWD
N
A
S
DADR
R
DATA n
A
DATA (n+1)
A
DATA (n+m)
DATA (n+m)-1
P
TWD
TXCOMP
Write START Bit
RXRDY
Write STOP Bit
after next-to-last data read
Read RHR
DATA n
Read RHR
DATA (n+1)
Read RHR
DATA (n+m)-1
Read RHR
DATA (n+m)