ATxmega16A4U Atmel Corporation, ATxmega16A4U Datasheet - Page 263

• Manufacturer Part Number: ATxmega16A4U
• Manufacturer: Atmel Corporation

Specifications of ATxmega16A4U

• Flash (kbytes): 16 Kbytes
• Pin Count: 44
• Max. Operating Frequency: 32 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 34
• Ext Interrupts: 34
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 7
• Twi (i2c): 2
• Uart: 5
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 12
• Adc Resolution (bits): 12
• Adc Speed (ksps): 2000
• Analog Comparators: 2
• Resistive Touch Screen: No
• Dac Channels: 2
• Dac Resolution (bits): 12
• Temp. Sensor: Yes
• Crypto Engine: AES/DES
• Sram (kbytes): 3.3
• Eeprom (bytes): 1024
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.6 to 3.6
• Operating Voltage (vcc): 1.6 to 3.6
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 5
• Output Compare Channels: 16
• Input Capture Channels: 16
• Pwm Channels: 16
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

21.3.7
8331A–AVR–07/11
Clock and Clock Stretching
Figure 21-5. Master write transaction.
Assuming the slave acknowledges the address, the master can start transmitting data (DATA)
and the slave will ACK or NACK (A/A) each byte. If no data packets are to be transmitted, the
master terminates the transaction by issuing a STOP condition (P) directly after the address
packet. There are no limitations to the number of data packets that can be transferred. If the
slave signals a NACK to the data, the master must assume that the slave cannot receive any
more data and terminate the transaction.
Figure 21-6 on page 263
action by issuing a START condition followed by an address packet with the direction bit set to
one (ADDRESS+R). The addressed slave must acknowledge the address for the master to be
allowed to continue the transaction.
Figure 21-6. Master read transaction.
Assuming the slave acknowledges the address, the master can start receiving data from the
slave. There are no limitations to the number of data packets that can be transferred. The slave
transmits the data while the master signals ACK or NACK after each data byte. The master ter-
minates the transfer with a NACK before issuing a STOP condition.
Figure 21-7
and write transactions separated by repeated START conditions (Sr).
Figure 21-7. Combined Transaction.
All devices connected to the bus are allowed to stretch the low period of the clock to slow down
the overall clock frequency or to insert wait states while processing data. A device that needs to
stretch the clock can do this by holding/forcing the SCL line low after it detects a low level on the
line.
S
S
S
ADDRESS
Address Packet #1
ADDRESS
ADDRESS
illustrates a combined transaction. A combined transaction consists of several read
Address Packet
Address Packet
R/W
A
Direction
illustrates the master read transaction. The master initiates the trans-
W
R
N Data Packets
DATA
A
A
Transaction
Transaction
A/A
DATA
DATA
Data Packet
Data Packet
Transaction
Sr
Atmel AVR XMEGA AU
ADDRESS
Address Packet #2
N data packets
N data packets
A
A
R/W
A
Direction
DATA
DATA
M Data Packets
DATA
A/A
A
A/A
P
P
263
P