Magtek InSpec 9000 Manuel d'utilisateur télécharger pdf (Page 66)

InSpec 9000 Encoded Card Tester

This means that if the character has an odd number of one bits in the character code for that

character, the parity bit is then a zero bit. On the other hand, if the character has an even number

of one bits in the character code for that character, the parity bit is a one bit causing the total

number of one bits to be odd. Thus the term odd parity.

Before the first character (or more specifically, the first series of bits that define the desired first

character) can be encoded, a Start Sentinel character needs to be encoded. The Start Sentinel is a

defined series of bits which signal the start of the data bits. Track 1 Start Sentinel consists of

seven bits (as all characters on Track 1). Track 2 Start Sentinel consists of five bits (as all

characters on Track 2). As an example, the Track 2 Start Sentinel code is: 11010.

After the last data character is encoded, an End Sentinel must be encoded. The End Sentinel is a

defined series of bits which signal the end of the data bits. Immediately after the End Sentinel, a

special error checking character is also encoded. This error checking character is called the LRC

- Longitudinal Redundancy Check character. For further details of the LRC see Appendix B,

Glossary of Terms.

Before the Start Sentinel character and after the LRC character, “clocking bits” are encoded.

These clocking bits provide card readers with timing to start their synchronization process before

encountering the start sentinel (or end sentinel for reverse reading). Figure A-9 illustrates the

relative location of all the characters previously discussed.

Figure A-9. Card Coding

Note that as you look at the diagram, while not to scale, the encoded information does travel

from right to left along the length of the magnetic stripe.

1 2 ... 61 62 63 64 65 66 67 68 69 70 71 ... 89 90

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Magtek InSpec 9000 Manuel d'utilisateur Page 66