Zebra TTPM3 Dokumentacja Pobierz pdf (Strona 59)

Programming

Command Reference

01/06/2009 TTPM3 Installation and Programming Manual P1003642-001

Additional Encoding Information

Checksum

To ensure correct reception of the message to be magnetically encoded, a checksum can be

appended to the data by the host computer. This checksum will then be compared by the

TTPM3 before encoding which guarantees that the magnetic code data is correctly received.

Calculate the checksum as the modulo 2 sum (consecutive XOR) of the ASCII data bytes sent

in the !M command. The checksum must have bit 7 set to 1 to distinguish it from ordinary

data.

Append the checksum at the end of the !M data string when encoding ISO data at track 2 (or

center track).

When the message has been received, the TTPM3 calculates the checksum and compares it to

the checksum appended to the message. If they are identical, an ACK is returned, otherwise a

NAK followed by the checksum calculated by the TTPM3 will be returned.

The checksum is never encoded on the magnetic stripe; it is only intended to secure data

transmission. The ISO format itself automatically adds a check digit to the magnetic code.

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Zebra TTPM3 Dokumentacja Strona 59