at91sam9263 ATMEL Corporation, at91sam9263 Datasheet - Page 485

• Manufacturer Part Number: at91sam9263
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

32.5
32.5.1
Figure 32-3.
Figure 32-4. Transfer Format
32.5.2
32.5.3
485
Functional Description
AT91SAM9263 Preliminary
Transfer format
Modes of Operation
Master Transmitter Mode
START and STOP Conditions
TWCK
TWD
The data put on the TWD line must be 8 bits long. Data is transferred MSB first; each byte must
be followed by an acknowledgement. The number of bytes per transfer is unlimited (see
32-4 on page
Each transfer begins with a START condition and terminates with a STOP condition (see
32-3 on page
The TWI has two modes of operation:
The TWI Control Register (TWI_CR) allows configuration of the interface in Master Mode. In this
mode, it generates the clock according to the value programmed in the Clock Waveform Gener-
ator Register (TWI_CWGR). This register defines the TWCK signal completely, enabling the
interface to be adapted to a wide range of clocks.
After the master initiates a Start condition when writing into the Transmit Holding Register,
TWI_THR, it sends a 7-bit slave address, configured in the Master Mode register (DADR in
TWI_MMR), to notify the slave device. The bit following the slave address indicates the transfer
direction, 0 in this case (MREAD = 0 in TWI_MMR).
The TWI transfers require the slave to acknowledge each received byte. During the acknowl-
edge 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 Not Acknowledge bit (NACK) in the status register if the slave does not
• A high-to-low transition on the TWD line while TWCK is high defines the START condition.
• A low-to-high transition on the TWD line while TWCK is high defines a STOP condition.
• Master transmitter mode
• Master receiver mode
Start Address R/W
TWCK
TWD
485).
485).
Start
Ack
Data
Ack
Data
Stop
Ack
Stop
6249D–ATARM–20-Dec-07
Figure
Figure