The RDM6300 reads RFID's with frequency of 125Khz.
The RDM6300 provides you with information on its serial port for the 125Khz chip's ID, but also with something called "version number" (The 2 and 3 byte).
I see it in a lot of libraries written for RDM6300, but I can't understand what it is for?
- arduino-rfid-RDM6300/arduino-rfid-RDM6300.ino at master · playfultechnology/arduino-rfid-RDM6300 · GitHub
- rdm6300/rdm6300.cpp at master · arduino12/rdm6300 · GitHub
RDM6300 Data Sheet: