at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 438

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

31.9.5.4
31.9.5.5
Figure 31-28. Clock Synchronization in Read Mode
Notes:
438
TWI_THR
TXCOMP
SVREAD
SCLWS
SVACC
TXRDY
TWCK
1. TXRDY is reset when data has been written in the TWI_THR to the shift register and set when this data has been acknowl-
2. At the end of the read sequence, TXCOMP is set after a STOP or after a REPEATED_START + an address different from
3. SCLWS is automatically set when the clock synchronization mechanism is started.
AT91SAM9G20 Preliminary
edged or non acknowledged.
SADR.
Clock Synchronization
Clock Synchronization in Read Mode
1
2
S
S
The data is memorized in TWI_THR until a new value is written
TWI_THR is transmitted to the shift register
The clock is stretched after the ACK, the state of TWD is undefined during clock stretching
As soon as a START is detected
SADR
In both read and write modes, it may happen that TWI_THR/TWI_RHR buffer is not filled /emp-
tied before the emission/reception of a new character. In this case, to avoid sending/receiving
undesired data, a clock stretching mechanism is implemented.
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 31-28 on page 438
DATA0
DATA0
R
Write THR
A
1
DATA0
A
describes the clock synchronization in Read mode.
DATA1
DATA1
CLOCK is tied low by the TWI
as long as THR is empty
A
XXXXXXX
2
DATA2
DATA2
Ack or Nack from the master
NA
S
6384B–ATARM–15-Dec-08