Memory card having improved data protection

• US 4,810,864 A
• Filed: 10/22/1987
• Issued: 03/07/1989
• Est. Priority Date: 11/07/1986
• Status: Expired due to Fees

• Current Assignee: Seiko Instruments Incorporated (Seiko Group)
• Original Assignee: Seiko Instruments Incorporated (Seiko Group)
• Inventors: Takahashi, Kaoru
• Primary Examiner(s): Paschall, M. H.
• Assistant Examiner(s): SALATA, ANTHONY J
• Application Number:
  US07/112,387
• Time in Patent Office: 502 Days
• Field of Search: 235/487, 235/380, 235/381, 235/492, 235/441, 361/111, 361/91, 361/57, 361/58, 361/54, 361/56
• US Class Current: 235/487
• CPC Class Codes: G11C 7/24 Memory cell safety or protection circuits, e.g. arrangements for preventing inadvertent reading or writing; Status cells; Test cells

Abstract

A memory card for storing information having a shape similar to that of a credit card. The memory card includes a capacitor connected across power terminals of a RAM and a resistor connected between one power terminal of the RAM and an external terminal. A switch is connected in parallel with the resistor for short-circuiting the resistor. The switch is controlled in accordance with a signal from an external device. When the RAM is accessed by the external device, the switch is closed so that the impedance of the power supply line is decreased.

Claims

1. A memory card having a shape similar to a credit card for storing information, said memory card being connectable to an external device which has a power source for supplying power at a given voltage, said memory card comprising:

memory means for storing information and having two internal power terminals for supplying power to said memory means and a plurality of internal information terminals for receiving and outputting information signals;

power supply means connected to said internal power terminals for supplying power to said memory means at a voltage different from the given voltage;

a plurality of external information terminals connected to said internal information terminals for electrically connecting said memory means to the external device;

two external power terminals;

means connected said external power terminals to said internal power terminals for electrically connecting said internal power terminals to the power source of the external device, said means including a resistor connected in series between one of said external power terminals and one of said internal power terminals;

a capacitor connected between said internal power terminals; and

switching means connectable to the external device to be actuated by a signal from the external device and connected to said resistor for short-circuiting said resistor in response to such signal.

2. A memory card as claimed in claim 1, wherein the values of said resistor and capacitor are selected so that the time constant constituted by said resistor and capacitor is larger than 1 msec.

3. A memory card as claimed in claim 1 further comprising a plurality of further resistors each connected between a respective one of said plurality of external information terminals and a respective one of said plurality of internal information terminals.