ATxmega64A3 Atmel Corporation, ATxmega64A3 Datasheet - Page 294

• Manufacturer Part Number: ATxmega64A3
• Manufacturer: Atmel Corporation

Specifications of ATxmega64A3

• Flash (kbytes): 64 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: 50
• Ext Interrupts: 50
• Usb Speed: No
• Usb Interface: No
• Spi: 10
• Twi (i2c): 2
• Uart: 7
• 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): 4
• Eeprom (bytes): 2048
• 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

25.5
25.6
8077H–AVR–12/09
Voltage reference selection
Conversion Result
As an example of the ADC channel scheme, one of the MUX/result register pairs can be setup to
do single-ended measurements triggered by event signal input, the second MUX/result pair can
measure a differential input on another event signal input, and the two last MUX/result pairs can
measure two other input sources started by the application software.
All the ADC channels use the same ADC for the conversions, but due to the pipelined design a
new conversion can be started on each ADC clock cycle. This means that multiple ADC conver-
sions can be progressing simultaneously and independently without changing the MUX settings.
A conversion result can be kept in one result register, independently of other result registers that
are continuously updated with new conversion results. This can help reduce software complex-
ity, and different software modules can start conversions and read conversion results fully
independent of each other.
The following voltages can be used as the voltage reference (VREF) for the ADC:
•
•
•
•
Figure 25-8. ADC voltage reference selection
The ADC can be set up to be either in signed or in unsigned mode. This setting is global for the
ADC and all ADC channels.
In signed mode, both negative and positive voltages can be measured, both for single ended
and differential input. With 12-bit resolution, the TOP value of a signed result is 2047 and the
results will be in the range -2048 to +2047 (0xF800 - 0x07FF). In unsigned mode the TOP value
is 4095 and results will be in the range 0 - 4095 (0 - 0x0FFF).
Signed mode must be used when any of the ADC inputs are set up for differential measure-
ments. In unsigned mode only single ended or internal signals can be measured.
The result of the analog to digital conversion is written to one of the result registers, RES.
In signed mode the ADC transfer function can be written as:
VINP and VINN are the positive and negative inputs to the ADC. GAIN is 1 unless differential
channels with gain is used.
In unsigned mode the ADC transfer functions can be written as:
Accurate internal 1.00V voltage.
Internal V
External voltage applied to AREF pin on PORTA.
External voltage applied to AREF pin on PORTB.
RES
=
CC
VINP - VINN
-------------------------------- - GAIN TOP
/1.6V voltage.
VREF
⋅
Internal VCC/1.6V
⋅
Internal 1.00V
AREFA
AREFB
VREF
XMEGA A
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