Method and circuit for manipulation-proof devaluation of EEPROMS

Details Method and circuit for manipulation-proof devaluation of EEPROMS Method and circuit for manipulation-proof devaluation of EEPROMS

1988-12-19

1991-03-19

Trafton, David

Registers

Records

Conductive

235436, 235441, G06K 1906

Patent

active

050013327

ABSTRACT:
A debit card includes at least one address and control logic circuit and a nonvolatile memory having a zone with memory locations provided for storing updated devaluation status of the debit card. At least part of the memory is electrically erasable and all of the memory locations of the zone of the nonvolatile memory can be read out and written upon bit by bit. A method and circuit for devaluation of a monolithically integrable electronic circuit of the debit card includes dividing the zone of the nonvolatile memory into partial zones each having a different value in the form of a multi-stage counter. A simultaneous erasure of the memory cells is permitted only for all of the memory cells of one partial zone of a given value. Erasure of each partial zone is permitted only after a transfer bit has been written into a previously unwritten memory cell of the partial zone of next-higher value. Writing-in is monitored with a logic circuit. An erasure of the partial zone of the highest value is permitted only under special conditions.

REFERENCES:
patent: 4572946 (1986-02-01), Schrenk
patent: 4648076 (1987-03-01), Schrenk
patent: 4680736 (1987-07-01), Schrenk
patent: 4853526 (1989-08-01), Effing
Handbuch der Modernen Datenverarbeitung; Forkel-Verlag; Book 136, Jul. 1987; "Einsatzmoglichkeiten der Chipkarte" (Merten Danneck).

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