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METHOD OF AND APPARATUS FOR PROVIDING A PROGRAMMABLE CLOCK FREQUENCY IN A SMART CARD INTERFACE

IP.com Disclosure Number: IPCOM000010154D
Publication Date: 2002-Oct-28

Publishing Venue

The IP.com Prior Art Database

Abstract

Generally, a smart card has a particular operating clock frequency that is selected before it is issued. The predominant frequency mode selected for smart cards is, for example, 4.9152 MHz in Japan and 3.579545 MHz in the U.S.A. and France. A prior art smart card write/reader therefore, has a clock generator implemented by an oscillator having a fixed frequency of 3.579545 MHz. The single-frequency clock generator scheme stated above is undesirable from the standpoint of applicable range. Specifically, when a smart card write/reader whose clock generator oscillates at a certain fixed clock frequency is loaded with a smart card that operates at a different frequency, the write/reader cannot read data out of the smart card at all so that the processing apparatus is practically useless. Another consideration relating to the clock signal is that, under some conditions, the duty cycle of the externally applied clock signal may vary, and parasitic effects may cause random transients (glitches) in the externally applied clock signal. The result of such duty cycle variation and/or glitches in the externally applied clock signal may be that the application program being run by the MPU does not execute properly, causing uncontrolled malfunctioning of the smart card. Another problem is the generation and application of selected clock frequencies in a smart card write/reader without exchanging components. When the prior art smart card write/reader whose clock generator oscillates at a certain fixed clock frequency is loaded with a smart card that operates at a different frequency, the write/reader cannot read data out of the smart card at all so that the processing apparatus is practically useless. What is needed is a way to generate and apply one of a selection of clock frequencies such that a given smart card reader can be utilized by smart cards of different operating frequencies. Also needed is a way to insure that random transients (glitches) and duty cycle variations do not occur when switching the externally applied clock signal from one clock frequency to another in a smart card write/reader as any variations in duty cycle or glitches present on the applied clock signal must be avoided. The result of any clock irregularities may be that the application program being run by the MPU does not execute properly, causing uncontrolled malfunctioning of the smart card. Thus, another need is a way to insure that there are no duty cycle variations and/or glitches present in the applied clock signal, in particular when the clock generator switches from one clock frequency to another.