ATxmega256A3B Atmel Corporation, ATxmega256A3B Datasheet - Page 208

• Manufacturer Part Number: ATxmega256A3B
• Manufacturer: Atmel Corporation

Specifications of ATxmega256A3B

• Flash (kbytes): 256 Kbytes
• Pin Count: 64
• Max. Operating Frequency: 32 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 47
• Ext Interrupts: 49
• Usb Speed: No
• Usb Interface: No
• Spi: 8
• Twi (i2c): 2
• Uart: 6
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 16
• Adc Resolution (bits): 12
• Adc Speed (ksps): 2000
• Analog Comparators: 4
• Resistive Touch Screen: No
• Dac Channels: 2
• Dac Resolution (bits): 12
• Temp. Sensor: Yes
• Crypto Engine: AES/DES
• Sram (kbytes): 16
• Eeprom (bytes): 4096
• 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: 7
• Output Compare Channels: 22
• Input Capture Channels: 22
• Pwm Channels: 22
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

19.3.3
19.3.4
19.3.5
19.3.6
8077H–AVR–12/09
Bit Transfer
Address Packet
Data Packet
Transaction
As illustrated by
period of the SCL line. Consequently the SDA value can only be changed during the low period
of the clock. This is ensured in hardware by the TWI module.
Figure 19-4. Data Validity
Combining bit transfers results in the formation of address and data packets. These packets
consist of 8 data bits (one byte) with the most significant bit transferred first, plus a single bit not-
acknowledge (NACK) or acknowledge (ACK) response. The addressed device signals ACK by
pulling the SCL line low, and NACK by leaving the line SCL high during the ninth clock cycle.
After the START condition, a 7-bit address followed by a read/write (R/W) bit is sent. This is
always transmitted by the Master. A slave recognizing its address will ACK the address by pull-
ing the data line low the next SCL cycle, while all other slaves should keep the TWI lines
released, and wait for the next START and address. The 7-bit address, the R/W bit and the
acknowledge bit combined is the address packet. Only one address packet for each START
condition is given, also when 10-bit addressing is used.
The R/W specifies the direction of the transaction. If the R/W bit is low, it indicates a Master
Write transaction, and the master will transmit its data after the slave has acknowledged its
address. Opposite, for a Master Read operation the slave will start to transmit data after
acknowledging its address.
Data packets succeed an address packet or another data packet. All data packets are nine bits
long, consisting of one data byte and an acknowledge bit. The direction bit in the previous
address packet determines the direction in which the data is transferred.
A transaction is the complete transfer from a START to a STOP condition, including any
Repeated START conditions in between. The TWI standard defines three fundamental transac-
tion modes: Master Write, Master Read, and combined transaction.
Figure 19-5
ing a START condition (S) followed by an address packet with direction bit set to zero
(ADDRESS+W).
SDA
SCL
illustrates the Master Write transaction. The master initiates the transaction by issu-
Figure 19-4
a bit transferred on the SDA line must be stable for the entire high
DATA
Valid
Change
Allowed
XMEGA A
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