Near Field Communication - technology that uses electromagnetic field to transfer information in a contactless way.
PCD
Proximity Coupling Device - reader device that supplies electromagnetic field to its antenna and uses it to communicate.
PICC
Proximity Integrated Circuit Card - tag device that captures electromagnetic field and uses it to power itself and to communicate.
UID
Unique IDentification number - sequence of bytes which is fixed and unique in original NFC tags.
BCC
Block Check Character - redundant byte in UID area used for error detection while reading UID.
OTP
One-Time Programmable - bits that can be changed only in one direction (0 to 1) in original NFC tags.
REQA
REQuest protocol A command - repeatedly issued by PCD to discover PICC devices.
ATQA
Answer To reQuest protocol A - values returned from PICC to PCD after receiving a REQA command. Fixed to 0x00 0x44 for MIFARE Ultralight.
SAK
Select AcKnowledge - value returned from PICC to PCD after completion of the anticollision procedure. Fixed to 0x00 for MIFARE Ultralight.
ACK
ACKnowledge - character returned from PICC to PCD usually upon successful write. Unlike other responses, this value is 4 bits long and equals 0xA.
NAK
Negative AcKnowledge - character returned from PICC to PCD usually upon a failed write due to permission restrictions set by lock bits. Unlike other responses, this value is 4 bits long and equals 0x0.
CRC
Cyclic Redundancy Check - mathematical algorithm used for error detection during data transfer, which appends 2 extra bytes at the end of a data message.
NDEF
NFC Data Exchange Format - format defined on NFC Forum to standartize data exchange in form of objects (text string, URL, WiFi connection credentials, application launch, etc.) rather than simply binary data.
APDU
Application Protocol Data Unit - logical request or response sequence between PCD and PICC communicating according to part 4 of ISO 14443 standard.
MIFARE Ultralight technology is not APDU-based. APDU are used with processor-based smartcards, contactless and with contacts.
PCB
Printed Circuit Board - material holding electronic components connected in a designed way.
