ATxmega256A3U Atmel Corporation, ATxmega256A3U Datasheet - Page 358

• Manufacturer Part Number: ATxmega256A3U
• Manufacturer: Atmel Corporation

Specifications of ATxmega256A3U

• 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: 50
• Ext Interrupts: 50
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• 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): 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

28.5
28.6
8331A–AVR–07/11
Voltage reference selection
Conversion Result
channels. This can help reduce software complexity, by allowing different software modules to
start conversions and read conversion results fully independently of each other.
The following voltages can be used as the reference (VREF) for the ADC:
•
•
•
•
•
Figure 28-8. ADC voltage reference selection
The result of the analog to digital conversion is written to the corresponding Channel result reg-
isters, RES. The ADC is either in signed or in unsigned mode. This setting is global for the ADC
and all ADC channels.
In signed mode, negative and positive results are generated. Signed mode must be used when
any of the ADC Channels are set up for differential measurements. In unsigned mode only sin-
gle ended or internal signals can be measured. 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).
The ADC transfer function can be written as:
VINP and VINN are the positive and negative inputs to the ADC.
For differential measurements GAIN is 1-64. For single ended and internal measurements GAIN
is always 1 and VINP is internal Ground.
In unsigned mode, only positive results are generated. The TOP value of of an unsigned result is
4095 and the results will be in the range 0 to +4095 (0x0 - 0x0FFF).
The ADC transfer functions can be written as:
VINP is the single ended or internal input.
ADC can be configured to generate either an 8-bit or a 12-bit result. A result with lower resolu-
tion will be available faster. See the
description on the propagation delay.
Accurate internal 1.00V voltage generated from the Bandgap
Internal V
Internal V
External voltage applied to AREF pin on PORTA
External voltage applied to AREF pin on PORTB
RES
RES
=
VINP - VINN
-------------------------------- - GAIN
CC
CC
=
/1.6V voltage
/2V voltage
VREF
VINP - (-ΔV )
--------------------------------- -
VREF
⋅
Internal VCC/2.0V
Internal VCC/1.6V
⋅
(
Internal 1.00V
TOP +1
⋅
(
TOP +1
AREFA
AREFB
)
)
”ADC Clock and Conversion Timing” on page 360
Atmel AVR XMEGA AU
VREF
for a
358