ATxmega128B1 Atmel Corporation, ATxmega128B1 Datasheet - Page 328

• Manufacturer Part Number: ATxmega128B1
• Manufacturer: Atmel Corporation

Specifications of ATxmega128B1

• Flash (kbytes): 128 Kbytes
• Pin Count: 100
• Max. Operating Frequency: 32 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 53
• Ext Interrupts: 53
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 3
• Twi (i2c): 1
• Uart: 2
• Segment Lcd: 160
• 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
• Temp. Sensor: Yes
• Crypto Engine: AES/DES
• Sram (kbytes): 8
• 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: 3
• Output Compare Channels: 10
• Input Capture Channels: 10
• Pwm Channels: 10
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

25.6
8291A–AVR–10/11
Conversion Result
Figure 25-8. ADC voltage reference selection
The result of the analog-to-digital conversion is written to the channel result register. The ADC is
either in signed or unsigned mode. This setting is global for the ADC and for the ADC channel.
In signed mode, negative and positive results are generated. Signed mode must be used when
the ADC channel is set up for differential measurements. In unsigned mode, only single-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 1/2 to 64. For single-ended and internal measurements,
GAIN is always 1 and VINP is the internal ground.
In unsigned mode, only positive results are generated. The TOP value 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.
The ADC can be configured to generate either an 8-bit or a 12-bit result. A result with lower res-
olution will be available faster. See the
description on the propagation delay.
The result register is 16 bits wide, and data are stored as right adjusted 16-bit values. Right
adjusted means that the eight least-significant bits (lsb) are found in the low byte. A 12-bit result
can be represented either left or right adjusted. Left adjusted means that the eight most-signifi-
cant bits (msb) are found in the high byte.
When the ADC is in signed mode, the msb represents the sign bit. In 12-bit right adjusted mode,
the sign bit (bit 11) is padded to bits 12-15 to create a signed 16-bit number directly. In 8-bit
mode, the sign bit (bit 7) is padded to the entire high byte.
Figure 25-9 on page 329
nal input range, and the result representation with 12-bit right adjusted mode.
RES
RES
=
VINP - VINN
-------------------------------- - GAIN
=
VREF
VINP - (-ΔV )
--------------------------------- -
VREF
⋅
Internal VCC/2.0V
Internal VCC/1.6V
⋅
to
(
Internal 1.00V
TOP +1
Figure 25-11 on page 329
⋅
(
TOP +1
AREFA
AREFB
)
)
”ADC Clock and Conversion Timing” on page 330
Atmel AVR XMEGA B
show the different input options, the sig-
VREF
for a
328