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Debit card read/write controller and process

  • US 6,581,831 B2
  • Filed: 12/18/2000
  • Issued: 06/24/2003
  • Est. Priority Date: 12/18/2000
  • Status: Active Grant
First Claim
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1. A process for reading and writing to a magnetic card stripe located on a card with a device comprising a magnetoresistive (MR) read head and a write head operatively connected to a microcontroller, and wherein the process comprises:

  • placing the read head and write head a distance of at least two bit cells apart and wherein the bit cell distance is the distance between a first clocking flux transition and a second clocking flux transition;

    initializing all memory locations in the microcontroller to their initial values;

    storing a timing value of said transition in a word in a memory at an address designated as current (CURR);

    if the detected edge is the first edge, a word in memory (called FIRST) is set to one and the content of the memory (CURR) is stored in an address designated as previous (PREV);

    waiting in a loop for the next transition to occur;

    allowing the next transition to occur;

    storing the transition time in CURR;

    calculating a current pulse time (TC) by calculating the difference between the two detected edges (transitions);

    calculating an expected pulse width (TE) from the previous pulse width (PREV);

    setting the TE to 75% of the PREV pulse width (TP) (TE0.75TP);

    comparing the value of the current pulse width (TC) with the value of the expected pulse width (TE);

    if the current pulse width (TC) is greater than the expected time (TE), a ZERO bit is detected;

    checking to see if FORCE is set to one, wherein if FORCE is set to one, a transition is forced to the output and FORCE is set to zero;

    setting the pulse width for ZERO bit (TZ) to equal the current pulse width (TC), and updating the previous pulse width (PREV) to the current pulse width.

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