Most reader devices do not return this value when the card is swiped to the presentation layer, and use it only to verify the input internally to the reader. This format was developed by the banking industry (ABA). This track is written with a 5-bit scheme (4 data bits + 1 parity), which allows for sixteen possible characters, which are the numbers 0-9, plus the six characters : ?.
The selection of six punctuation symbols may seem odd, but in fact the sixteen codes simply map to the ASCII range 0x30 through 0x3f, which defines ten digit characters plus those six symbols. Start sentinel - one character (generally ‘ ’).Primary account number (PAN) - up to 19 characters.Usually, but not always, matches the credit card number printed on the front of the card. The first digit specifies the interchange rules, the second specifies authorization processing and the third specifies the range of services.
