Datasheet

708
SAM4S Series [DATASHEET]
11100F–ATARM–29-Jan-14
34.10.5.4 Clock Synchronization
In both read and write modes, it may happen that TWI_THR/TWI_RHR buffer is not filled /emptied before the
emission/reception of a new character. In this case, to avoid sending/receiving undesired data, a clock stretching
mechanism is implemented.
Clock Synchronization in Read Mode
The clock is tied low if the shift register is empty and if a STOP or REPEATED START condition was not detected. It is
tied low until the shift register is loaded.
Figure 34-28 describes the clock synchronization in Read mode.
Figure 34-28. Clock Synchronization in Read Mode
Notes: 1. TXRDY is reset when data has been written in the TWI_THR to the shift register and set when this data has been
acknowledged or non acknowledged.
2. At the end of the read sequence, TXCOMP is set after a STOP or after a REPEATED_START + an address different
from SADR.
3. SCLWS is automatically set when the clock synchronization mechanism is started.
Clock Synchronization in Write Mode
The clock is tied low if the shift register and the TWI_RHR is full. If a STOP or REPEATED_START condition was not
detected, it is tied low until TWI_RHR is read.
Figure 34-29 describes the clock synchronization in Read mode.
DATA 1
The clock is stretched after the ACK, the state of TWD is undefined during clock stretching
SCLWS
SVACC
SVREAD
TXRDY
TWCK
TWI_THR
TXCOMP
The data is memorized in TWI_THR until a new value is written
TWI_THR is transmitted to the shift register
Ack or Nack from the master
DATA 0DATA0 DATA 2
1
2
1
CLOCK is tied low by the TWI
as long as THR is empty
S
SADR
S
R DATA0A
A
DATA 1
A DATA 2 NA S
XXXXXXX
2
Write THR
As soon as a START is detected