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.

Title
Proximity data transfer system with tamper proof portable data token
Application Number
05/322,669
Publication Number
3906460
Application Date
January 11, 1973
Publication Date
September 16, 1975
Inventor
Halpern John W
Agent
Townsend and Townsend
IPC
G06k 19/00
G06k 01/14
G07f 07/02
G06K 19/73
G07F 07/08
G07F 07/10
G06Q 40/00
View Original Source