Device for communicating with a portable data medium

A device for communicating with a portable data medium using at least a power signal (AL) supplied by an electric energy source (4), a control signal (SC1) and a data transmission signal (I/O), comprises an interrupter (5) for interrupting the power signal (AL) to the medium from the source if the portable data medium does not cooperate with the device (1), means (8) for storing electric energy received from the source and for supplying the power signal to the medium when the source does not supply power and a data processor (3) arranged to ensure transmission of the power, control and data transmission signals (AL, SC1, I/O) to the medium according to a predetermined sequencing, as well as for detecting the interruption of the power signal (AL) from the source, then for triggering the interruption of the control and data transmission signals (SC1, I/O) according to the predetermined sequencing during the supply of the power signal from the energy storage mean.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to a device for communicating with a portable data
 medium in a communication using at least a power signal supplied by an
 electric energy source, a control signal and a data transmission signal.
 2. Description of Related Art
 Typically, the portable data medium can be a chip card incorporating a
 microprocessor or microwired logic circuits defining areas to which access
 is controlled and thus capable of containing secret information such as
 cryptographic keys (see for example the portable object described in U.S.
 Pat. No. 4,211,919).
 The object of the invention is to offer an original solution for solving
 the general problem of the sequencing of the signals, particularly so as
 to comply with the standards applicable in this case (for example ISO
 standard 7816-3). It makes it possible, in a simple way, to meet the
 contradictory requirements of detecting the interruption of the power
 signal if the portable data medium is removed, and of continuing to supply
 this signal to the portable data medium for a given time after this
 detection.
 SUMMARY OF THE INVENTION
 For this purpose, the device according to the invention comprises:
 interrupting means disposed between the electric energy source and the
 portable data medium and controlled by the latter so that they interrupt
 the supply of the power signal to the portable data medium from the
 electric energy source if the portable data medium is not cooperating with
 the device and so that they allow this supply if the portable data medium
 is cooperating with the device;
 energy storage means designed to store the electric energy received from
 the electric energy source, connected to a power supply input of the
 portable data medium so as to supply this power signal to the latter for a
 predetermined time following an interruption of this supply of the power
 signal from the electric energy source;
 data processing means designed to ensure transmission to the portable data
 medium of the signals according to a predetermined sequencing, and to
 interrupt this transmission according to a predetermined sequencing, as
 well as to detect the interruption of the supply of the power signal from
 the electric energy source, then trigger the interruption of the other
 signals according to this predetermined sequencing while the power signal
 is supplied from the energy storage means.

FIG. 1 shows a device 1 intended to cooperate with a portable data medium
 2. The device 1 comprises data processing means 3 in the form of a
 microprocessor or microwired logic circuits, including means for storing
 the data. These data processing means 3 comprise means designed to manage
 communication with the portable data medium 2, and particularly to control
 a plurality of signals, indicated below, used to conduct this
 communication in such a way that the latter appear and disappear according
 to a predetermined sequencing, in accordance with any standard that may be
 applicable. In the case of a microprocessor, these means comprise a
 specific program. In the case of microwired logic circuits, they comprise
 specific microwired logic circuits.
 The device 1 also comprises an electric energy source 4 connected to data
 processing means 3 and to the portable data medium 2 through a portable
 data medium presence switch 5 connected in series with reverse-locking
 means 6. These reverse-locking means 6 are connected to a power supply
 input 7 of the portable data medium 2 intended to receive a power signal
 AL. The electric energy source 4 can for example comprise a voltage source
 constituted by an electric generator such as a battery, a photovoltaic
 cell, or a very high-capacity capacitor. In a less preferred variant of
 embodiment, the electric energy source 4 is outside the device 1.
 The medium presence switch 5 is such that it closes when the portable data
 medium 2 is inserted into a connector equipping the device 1 and designed
 to receive the portable data medium 2. The device 1 also comprises energy
 storage means 8 connected to an output 14 of the reverse-locking means 6
 and designed to store the electric energy received from the electric
 energy source 4. The reverse-locking means 6 are designed to prevent a
 return of electric energy from the energy storage means 8 to the delivery
 means 11. They comprise for example a diode, a transistor, or a regulating
 circuit designed to carry out this function.
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The device 1 also comprises a delivery accelerator 9 connected at one end
 to energy storage means 8, and comprising on the other end a terminal 10
 through which it is connected to the data processing means 3. The delivery
 accelerator 9 is designed to draw on the energy storage means 8 for the
 flow of electric energy, while being controlled by the data processing
 means 3. It comprises for example a resistor, a transistor or combination
 of transistors, or a logic gate.
 The above-mentioned delivery means 11 comprise an input connected to an
 input 12 of the reverse-locking means 6 through which the latter is itself
 connected to the medium presence switch 5, and an output which drives an
 interrupting input 13 of the data processing means 3. These means are
 designed to instantaneously deliver the electric energy present in the
 terminal 12 when the medium presence switch 5 is opened, so that the data
 processing means 3 detects this opening. They comprise for example one or
 more resistors, or one or more transistors. These delivery means 11 are
 only necessary in cases where, in practice, a zero capacity cannot be
 obtained in the terminal 12 due to the components used, and where it is
 consequently necessary to deliver this capacity.
 The reverse-locking means 6, like the delivery means 11, can be replaced by
 any other means for detecting the stopping of the supply of the power
 signal AL from the electric energy source 4 located at any place in the
 device 1 that will enable it to achieve this detection. These means can be
 zero current measuring means between the electric energy source 4 and the
 energy storage means 8, for example using optical or inductive means.
 The device 1 also preferably comprises adapting means 15 for supplying the
 portable data medium 2 with the control signals SC1 and SC2, and for
 exchanging with it a data transmission signal I/O. These adapting means 15
 are intended to use these signals in accordance with any standard that may
 be applicable.
 Naturally, the various means of the device 1 defined above could be
 physically located on the same, single component having a microprocessor
 or microwired logic circuits, and not necessarily on separate components.
 In operation, when the portable data medium 2 is inserted into the device
 1, the medium presence switch 5 closes, causing the following effects:
 the input 12 of the reverse-locking means 6 goes from a low level of
 electric energy to a high level of electric energy;
 the delivery means 11 feed back to the input 13 of the data processing
 means 3 this high level of electric energy, thus informing it that the
 portable data medium 2 has been inserted and that it is necessary to start
 a procedure for communicating with it;
 the energy storage means 8 are charged;
 the portable data medium 2 receives, through its power supply input 7, the
 electric energy that allows it to operate;
 the delivery accelerator 9 is maintained in the inactive position by the
 data processing means 3, which act on the terminal 10;
 the data processing means 3 are designed to cause the appearance of the
 signals I/O, SC1, SC2 according to a predetermined sequencing, in
 accordance with any standard that may be applicable.
 The device 1 and the portable data medium 2 are then ready to run a
 dialogue procedure.
 When the portable data medium 2 is subsequently extracted from the device
 1, the medium presence switch 5 opens, causing the following effects:
 the input 12 of the reverse-locking means 6 goes from a high level of
 electric energy to a low level of electric energy;
 the delivery means 11 feed back to the input 13 of the data processing
 means 3 this low level of electric energy, which is detected by the data
 processing means 3, which interrupt any processing operation in progress
 to trigger a suppression of the signals I/O, SC1, SC2 according to a
 predetermined sequencing, in accordance with the applicable standard;
 next, the delivery accelerator 9 controlled by the data processing means 3
 through its terminal 10, discharges the energy storage means 8, which has
 the effect of bringing the electric energy available at the power supply
 input 7 of the portable data medium 2 to zero, in order to prepare for its
 disconnection from the device 1.
 In FIG. 2, the elements that are homologous to those in FIG. 1 have the
 same references. The data processing means 3 comprise a microprocessor,
 the electric energy source 4 comprises two batteries connected in series,
 and the delivery means 11 comprise two resistors R1, R2 connected in
 series between the terminal 12 of the voltage regulator 6 and a ground of
 the device 1, a common point of these resistors being connected to the
 terminal 13 of the microprocessor. The reverse-locking means 6 comprise a
 linear voltage regulator or "low drop out" regulator having the property
 of supplying a slight voltage drop on output; an identical voltage
 regulator 6A is interposed between the electric energy source 4 and the
 microprocessor 3.
 The energy storage means (8) comprises a capacitor 8A connected between the
 terminal 14 of the voltage regulator and the ground. The delivery
 accelerator comprises a resistor 9 connected between the terminal 14 and
 the microprocessor.
 The power signal AL is represented by a voltage signal VCC; the control
 signals comprise a clock signal CLK and a reset signal RST.
 The portable data medium is represented by a chip card 2 of the credit card
 type.
 In a preferred embodiment, the device 1 is portable and is the same size as
 a chip card holder, while the microprocessor 3 is also provided with a
 display 16 and is designed so that, once the chip card 2 is inserted into
 the connector of the device 1, the display 16 automatically displays an
 account balance located on the chip card 2, possibly in addition to other
 information. The device 1 can then advantageously constitute a personal
 balance reader which does not require any particular keying from the user.
 Generally, exchanges of data with a chip card are codified by ISO standard
 7816, wherein part 7816-3 relates to the sequencing of the various signals
 applied to the chip card, namely the ground reference signal GND, the
 power signal VCC, the memory power signal VPP, the clock signal CLK, the
 reset signal RST, and the data exchange signal I/O, as shown in the timing
 chart in FIG. 3.
 It may be seen that during the establishment of the exchange, the signals
 VCC, VPP, CLK and RST must be supplied in this order; the signal VPP,
 which is not generally used, is then short-circuited by connecting with
 the signal VCC. At the end of the exchange, the above-mentioned signals
 must disappear in the reverse order.
 In FIG. 4, a "card presence" curve defines the disposition of the chip card
 2 relative to the device 1 (inserted or extracted), and another "point 12"
 curve defines the change in the voltage at point 12 in FIG. 2. Finally, a
 third diagram represents several overlapping curves. When the chip card 2
 is inserted, the voltage signal VCC, the data transmission signal I/O, the
 clock signal CLK, and the reset signal RST appear in succession, and when
 the card is removed, these signals disappear in the reverse order.
 While the sequencing of the appearance of the signals is managed by a
 specific program of the microprocessor, the sequencing of the
 disappearance of these signals also involves the electronic means in FIG.
 2.
 The curve of the voltage signal VCC encompasses all the other curves. When
 the card is removed, it decreases in two phases corresponding to two
 successive time constants: .tau.1=1000 .mu.s and .tau.2=50 .mu.s, in
 compliance with a drop limit imposed by ISO standard 7816-3 and
 represented in the figure: VCC &lt;0.4 V after 500 .mu.s following the card
 removal.
 The fact that the signals I/O, RST, CLK are produced from a voltage of the
 microprocessor, which itself is derived from the voltage VCC supplied to
 the latter, guarantees that their level is always lower than that of VCC.
 The resistors R1, R2 make it possible, in association with the voltage
 regulator 6, to detect the card removal. The capacitor 8A makes it
 possible to continue to supply power to the chip card 2 while the signals
 I/O, RST, CLK are reset to zero, which occurs within the phase with the
 time constant .tau.1, and the resistor 9, in association with the
 microprocessor, makes it possible to accelerate the decrease of VCC after
 this reset, in the phase with the time constant .tau.2.
 While this invention has been described in conjunction with specific
 embodiments thereof, it is evident that many alternatives, modifications
 and variations will be apparent to those skilled in the art. Accordingly,
 the preferred embodiments of the invention as set forth herein, are
 intended to be illustrative, not limiting. Various changes may be made
 without departing from the true spirit and full scope of the invention as
 set forth herein and defined in the claims.