ATxmega256A3U Atmel Corporation, ATxmega256A3U Datasheet - Page 36

• 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

19. RTC - 16-bit Real-Time Counter
19.1
19.2
8386A–AVR–07/11
Features
Overview
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The 16-bit Real Time Counter (RTC) is a counter that typically runs continuously, including in
low power sleep modes, to keep track of time. It can wake up the device from sleep modes
and/or interrupt the device at regular intervals.
The reference clock is typically the 1.024kHz output from a high accuracy crystal of 32.768kHz,
and this is the configuration most optimized for low power consumption. The faster 32.768kHz
output can be selected if the RTC needs a higher resolution than 1mS. The RTC can also be
clocked from an external clock signal, the internal 32.768kHz oscillator or the internal 32kHz
ULP oscillator.
The RTC includes a 10-bit programmable prescaler that can scale down the reference clock
before it reaches the Counter. A wide range of resolution and time-out periods can be config-
ured. With a 32.768kHz clock source the maximum resolution of 30.5µs, time-out periods range
up to 2000seconds. With a resolution of 1 second, the maximum time-out period is over 18hours
(65536seconds). The RTC can give a compare interrupt and/or event when the counter equals
the Compare register value, and an overflow interrupt and/event when it equals the Period regis-
ter value.
Figure 19-1. Real-time Counter overview
16-bit resolution
Selectable clock source
Programmable 10-bit clock prescaling
One Compare register
One Period register
Clear Counter on period overflow
Optional Interrupt/ Event on overflow and compare match
– 32.768kHz external crystal
– External clock
– 32.768kHz internal oscillator
– 32kHz internal ULP oscillator
TOSC1
TOSC2
32.768kHz Crystal Osc
32kHz int ULP (DIV32)
32.768kHz Int. Osc
External Clock
RTCSRC
prescaler
10-bit
clk
RTC
COMP
PER
CNT
XMEGA A3U
=
=
Compare
Overflow
”match”/
TOP/
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