![](http://datasheet.mmic.net.cn/100000/IF180C52TXXX-20R_datasheet_3493957/IF180C52TXXX-20R_500.png)
500
32099I–01/2012
AT32UC3L016/32/64
22.8.7
Wakeup from Sleep Modes by TWI Address Match
The TWIS is able to wake the device up from a sleep mode upon an address match, including
sleep modes where CLK_TWIS is stopped. After detecting the START condition on the bus, The
TWIS will stretch TWCK until CLK_TWIS has started. The time required for starting CLK_TWIS
depends on which sleep mode the device is in. After CLK_TWIS has started, the TWIS releases
its TWCK stretching and receives one byte of data on the bus. At this time, only a limited part of
the device, including the TWIS, receives a clock, thus saving power. The TWIS goes on to
receive the slave address. If the address phase causes a TWIS address match, the entire
device is wakened and normal TWIS address matching actions are performed. Normal TWI
transfer then follows. If the TWIS is not addressed, CLK_TWIS is automatically stopped and the
device returns to its original sleep mode.
22.8.8
Identifying Bus Events
This chapter lists the different bus events, and how these affects the bits in the TWIS registers.
This is intended to help writing drivers for the TWIS.
Table 22-5.
Bus Events
Event
Effect
Slave transmitter has sent a
data byte
SR.THR is cleared.
SR.BTF is set.
The value of the ACK bit sent immediately after the data byte is given
by CR.ACK.
Slave receiver has received
a data byte
SR.RHR is set.
SR.BTF is set.
SR.NAK updated according to value of ACK bit received from master.
Start+Sadr on bus, but
address is to another slave
None.
Start+Sadr on bus, current
slave is addressed, but
address match enable bit in
CR is not set
None.
Start+Sadr on bus, current
slave is addressed,
corresponding address
match enable bit in CR set
Correct address match bit in SR is set.
SR.TRA updated according to transfer direction (updating is done one
CLK_TWIS cycle after address match bit is set)
Slave enters appropriate transfer direction mode and data transfer
can commence.
Start+Sadr on bus, current
slave is addressed,
corresponding address
match enable bit in CR set,
SR.STREN and SR.SOAM
are set.
Correct address match bit in SR is set.
SR.TRA updated according to transfer direction (updating is done one
CLK_TWIS cycle after address match bit is set).
Slave stretches TWCK immediately after transmitting the address
ACK bit. TWCK remains stretched until all address match bits in SR
have been cleared.
Slave enters appropriate transfer direction mode and data transfer
can commence.
Repeated Start received
after being addressed
SR.REP set.
SR.TCOMP unchanged.
Stop received after being
addressed
SR.STO set.
SR.TCOMP set.