Atmel Xplained Pro Evaluation Kit for the ATSAMD21J18A Microcontroller ATSAMD21-XPRO ATSAMD21-XPRO Data Sheet

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Atmel | SMART SAM D21 [DATASHEET]

Atmel-42181C–SAM-D21_Datasheet–07/2014

 contains acronyms and abbreviations used in this document. 

R/W

Read/Write accessible register bit. The user can read from and write to this bit. 

R

Read-only accessible register bit. The user can only read this bit. Writes will be ignored. 

W

Write-only accessible register bit. The user can only write this bit. Reading this bit will return an 
undefined value. 

BIT

Bit names are shown in uppercase. (Example PINA1)

BITS[n:m] 

A set of bits from bit n down to m. (Example: PINA3..0 = {PINA3, PINA2, PINA1, PINA0}

Reserved

Reserved bits are unused and reserved for future use. For compatibility with future devices, always 
write reserved bits to zero when the register is written. Reserved bits will always return zero when 
read. 

PERIPHERALi

If several instances of a peripheral exist, the peripheral name is followed by a number to indicate the 
number of the instance in the range 0-n. PERIPHERALi denotes one specific instance. 

Reset 

Value of a register after a power reset. This is also the value of registers in a peripheral after

performing a software reset of the peripheral, except for the Debug Control registers.

SET/CLR

Registers with SET/CLR suffix allows the user to clear and set bits in a register without doing a read-
modify-write operation. These registers always come in pairs. Writing a one to a bit in the CLR 
register will clear the corresponding bit in both registers, while writing a one to a bit in the SET 
register will set the corresponding bit in both registers. Both registers will return the same value when 
read. If both registers are written simultaneously, the write to the CLR register will take precedence. 

AC

Analog Comparator

ADC

Analog-to-Digital Converter

ADDR

Address

AHB

AMBA Advanced High-performance Bus

APB

AMBA Advanced Peripheral Bus

AREF

Analog reference voltage

AV

DD

Analog supply voltage

BLB

Boot Lock Bit

BOD

Brown-out detector

CAL

Calibration

CC

Compare/capture

CLK

Clock

CRC

Cyclic Redundancy Check