ATxmega128B1 Atmel Corporation, ATxmega128B1 Datasheet - Page 330

• 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

25.8
25.8.1
25.9
8291A–AVR–10/11
Starting a Conversion
ADC Clock and Conversion Timing
Input Source Scan
Before a conversion is started, the input source must be selected. An ADC conversion can be
started either by the application software writing to the start conversion bit or from any events in
the event system.
It is possible to select a range of consecutive input sources that is automatically scanned and
measured when a conversion is started. This is done by setting the first (lowest) positive ADC
channel input using the MUX control register, and a number of consecutive positive input
sources. When a conversion is started, the first selected input source is measured and con-
verted, then the positive input source selection is incremented after each conversion until it
reaches the specified number of sources to scan.
The ADC is clocked from the peripheral clock. The ADC can prescale the peripheral clock to pro-
vide an ADC Clock (clk
operating range of the ADC.
Figure 25-12. ADC prescaler.
The maximum ADC sample rate is given by the he ADC clock frequency (f
sample a new measurement on every ADC clock cycle.
The propagation delay of an ADC measurement is given by:
RESOLUTION is the resolution, 8 or 12 bits. The propagation delay will increase by one extra
ADC clock cycle if the gain stage (GAIN) is used.
The propagation delay is longer than one ADC clock cycle, but the pipelined design means that
the sample rate is limited not by the propagation delay, but by the ADC clock rate.
The most-significant bit (msb) of the result is converted first, and the rest of the bits are con-
verted during the next three (for 8-bit results) or five (for 12-bit results) ADC clock cycles.
Converting one bit takes a half ADC clock period. During the last cycle, the result is prepared
before the interrupt flag is set and the result is available in the result register for readout.
Sample Rate
Propagation Delay =
=
f
ADC
1
--------------------------------------------------------------------- -
+
RESOLUTION
-------------------------------------- -
ADC
PRESCALER[2:0]
) that matches the application requirements and is within the
2
f
ADC
Clk
PER
+
GAIN
9-bit ADC Prescaler
Atmel AVR XMEGA B
Clk
ADC
ADC
). The ADC can
330