ATXMEGA128A4U-AU Datasheet, PDF (52/121 Pages) ATMEL Corporation – 8/16-bit Atmel XMEGA A4U Microcontroller

31.1.5 Communication functions
31.1.6
SCL
SDA
XCKn
RXDn
TXDn
SS
MOSI
MISO
SCK
D-
D+
Serial Clock for TWI
Serial Data for TWI
Transfer Clock for USART n
Receiver Data for USART n
Transmitter Data for USART n
Slave Select for SPI
Master Out Slave In for SPI
Master In Slave Out for SPI
Serial Clock for SPI
Data- for USB
Data+ for USB
Oscillators, Clock and Event
31.1.7
TOSCn
XTALn
CLKOUT
EVOUT
RTCOUT
Debug/System functions
Timer Oscillator pin n
Input/Output for Oscillator pin n
Peripheral Clock Output
Event Channel 0 Output
RTC Clock Source Output
RESET
PDI_CLK
PDI_DATA
Reset pin
Program and Debug Interface Clock pin
Program and Debug Interface Data pin
XMEGA A4U
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8387A–AVR–07/11