Here is a brief explanation of formats associated with proximity cards
Parity Bits -Most of the proximity cards/tokens contain at least 1 error detection or parity bit. This bit is used to count the number of zeroes or ones contained on the card. If this bit is zero, it typically is referring to the fact there are an even number of zeroes or ones on the card.
Site codes or families were originally created to provide for the production of a larger number of "26 bits" cards by duplicating cards rather than increasing the available number of user codes.
The cards were ordered for a specific site and the manufacturers, in the beginning, were keeping track of what had been shipped where. When a new site was installed, the site was provided with a site code that had never shipped to that immediate geographic area, thus, maintaining the level of security of the card. Also, the fact that all the cards on a specific site had the same site code, the control equipment did not have to store the site code in each of the user's code, thus reducing memory requirements in the hardware.
Identification Code - This is the employee ID number. Often times this is printed on the card.
Standard 26 Bit Format Structure:
The standard 26 bit Wiegand format is H10301. It is binary encoded data. The format consists of 2 parity bits, 8 bit facility code (F) and 16 bit card number fields (B). The format is shown below.
PFFFFFFFFBBBBBBBBBBBBBBBBP
EXXXXXXXXXXXX.............
.............XXXXXXXXXXXXO
Bit Coding
P = Parity
O = Odd Parity
E = Even Parity
X = Parity mask
F = Facility code, range = 0 to 255
B = Card Number, range = 0 to 65,535
26 Bit Format
General: The 26-bit format is the industry standard format, and is an open format. The sale of this format is not limited to any one company. The range of card numbers available in this format is limited and therefore there is a potential for card numbers to be duplicated. It is important to understand that HID does not insure that card numbers will not be duplicated. HID does not control or restrict the ordering of cards encoded with the standard 26 bit format. Convenience in ordering cards and universal access control panel acceptance are the primary benefits in using the standard 26 bit card format.
Description: The 26-bit format consists of 255 possible facility codes. Within each facility code there is a total of 65,535 unique card number.