Abstract: Each card of a set of credit cards includes a memory having plural memory fields. The memory of each card in a set includes a first unalterable multi-bit field indicative of an identification of an external means with which the card can be used, as well as a second unalterable mutli-bit field indicative of operations that can be performed with the card on the external means and an alterable multi-bit field indicative of the number of credit units available to a card holder. Each card includes circuits for controlling the memory, and means for temporarily coupling the memory and circuits to the external means. Each of the first and second unalterable bit fields includes n bits. A change from one bit state to the other bit state of a predetermined number, m, of bits in the unalterable fields of each card in the set is irreversible after imprinting, where m is equal to or less than n.

Abstract: An arrangement for both exchanging data between first and second devices and supplying power from the first to the second device, all through only two interconnecting lines or contacts. Data transmission from the first to second device is accomplished by a modulated current generator in the first device connected to the two liens. Data transmission from the second to the first device is accomplished by a modulator which shunts the two lines while the current generator supplies a current, thus varying the voltage across the line in a manner which may be sensed by a comparator in the first device. In order to supply power to the second device, the second device includes a network having at least one unidirectional conduction member, such as a diode, connected to the two lines.

Abstract: A credit card system includes a credit card containing a memory for storing coded information indicative of: an identification of the use for which the article is intended, an identification of units used to keep account of operations which are performed in connection with the credit card, and the number of units available to a holder of the credit card. The memory is structured so that the two identification data zones have bits wherein a change from one binary value to another is irreversible, to prevent tampering of the identification of the card. The card also includes circuits for controlling the memory and contacts for temporarily coupling the card to an imprinting and/or operating means that are respectively coupled to the card at the time it is purchased and when it is being used to purchase goods or services. When the card is purchased, the number of units is imprinted onto the card in the third zone, and the number of these units is decremented as the card is being used.

Abstract: A system for keeping account of predetermined homogeneous units by means of an article such as a card, carrying information which may be the amount of a credit balance, and an external device for operating on the information. In general, the balance on the card is initially validated. Thereafter, the balance is irrevocably drawn upon as desired until a zero balance is reached. In order to avoid a single large expenditure to validate the card, and at the same time to minimize the possibility of fraud, a memory in the card has a plurality of zones which are individually validatable. A separate validating field in the memory has validating bits corresponding to individual memory zones. The validity field is accessible by the external device only, and is protected by a coded key embodied in the card. To make the system usable for recording other than whole numbers of units, one of the zones may have a plurality of sub-zones. One of the sub-zones may be allocated to multiples or sub-multiples of individual units.