3906460 is referenced by 173 patents and cites 12 patents.

A data handling system comprising a data transfer portion and a portable data token portion. The data transfer portion includes means for transferring data between the data token and a computer, data checking circuitry, means for transferring a validation character signal to the data token, and a program counter for sequencing the data transfer portion components. The data token portion includes a data register, means for storing and fetching data in the data register in cooperation with the data transfer means in the data transfer portion, a validation circuit for preventing alteration of the contents of the data register unless a correct validation character signal is received by the data token portion, and means for rendering the data token portion permanently inoperative after a number of incorrect validation character signals are received thereby. Visual indicators in the data token portion signify that the data in the token register has fallen below a predetermined threshold value and that the data token has been permanently disabled.

Proximity data transfer system with tamper proof portable data token
Application Number
Publication Number
Application Date
January 11, 1973
Publication Date
September 16, 1975
Halpern John W
Townsend and Townsend
G06k 19/00
G06k 01/14
G07f 07/02
G06K 19/73
G07F 07/08
G07F 07/10
G06Q 40/00
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