FR2707027A1 - Electronic and portable device for counting units - Google Patents

Abstract

The present invention relates to a portable device for counting units in bits with an erasable and rewritable electronic memory for storing the said consumable units which provide a user with entitlements to services or products. To avoid fraudulent activities, the invention proposes a portable device which allows improved management of the units and which requires no redundancy but which avoids any anomalous result in the event of early removal.

Description

ELECTRONIC AND PORTABLE DEVICE
OF COUNTING UNITS
The present invention relates to a portable device for counting bit units with an erasable and rewritable electronic memory for storing said units.

More specifically, the invention particularly relates to such a portable device such as for example a card with a memory containing consumable units which give a user titles to services or products.

Such calling cards are known for payphones for example, the first generation of which used the so-called "token" counting method, consisting in irreversibly changing the state of a bit to count a unit. This method corresponded to the possibilities of the so-called memories
EPROM. It had the advantage of being easily secured, a unit counter being able to progress only in one direction.

The method has three drawbacks, however.

On the one hand, recharging is impossible. On the other hand, the number of units has been severely limited by the memory size of the component. Finally, access to the memory is done sequentially, which requires relatively complex software in the payphone and, in some cases, a relatively long access time to the relevant bits.

Another generation of cards has solved these problems. It uses EEPROM memory cells and a so-called "abacus" counting method.

This second generation also has drawbacks.

First, the number of possible units in an EEPROM memory cell is often limited (typically 10,000 erase write cycles). Counting a higher number therefore requires redundancy, which again increases the memory size, as well as a complex logic circuit.

Second, these cards are generally visible in the reader, and can be removed by a user at any time. If this happens during the writing process, the result can be profoundly altered. In certain cases, the memory is erased by words before being rewritten, the counter can therefore be reset to zero. In some configurations of the counter, bits must be written on the one hand and erased on the other. Removing the card between these two moments can lead to an aberrant result: partial reloading of the card, consumption of too many units. Here again, redundancies and expensive specialized circuits are therefore used.

To avoid these problems set out above, the object of the invention is to provide a portable device which allows improved management of the units and which requires no redundancy but which avoids any aberrant result in the event of early withdrawal.

In order to achieve this aim, the invention proposes such a portable device for counting units in bits, with an erasable and rewritable electronic memory for storing said units, also comprising a logic circuit which counts the units in a way that the counting of a unit only involves a change of state of a single bit and in that the counting memory and the logic increment (or decrement) circuit are on a single electronic component.

Also, the portable device according to the invention gives other additional advantages - A capacity is also always obtained without redundancy
counting greater than the number of cycles
erase-write memory cells.

- Finally, the invention makes it possible to simplify the orders
write to the card, and in some cases
accelerate.

Other features of the invention will become apparent from the claims.

The invention will be better understood on reading the description of several embodiments of the invention given by way of nonlimiting examples.

The counting device has n bits of EEPROM or any other type of electrically erasable memory. Rather than using the usual counting method, where the rank bit weighs 2p, the device according to the invention uses a reflected code. The essential advantage of this system is that the incrementation of the counter (or its decrementation) is done by changing a single bit.

Here is an example of a counter of this type, on 3 bits
VALUE USUAL CODIFICATION INVENTIVE CODIFICATION
0,000,000
1,001,001
2,010,011
3,011,010
4,100,110
5,101,111
6 110 101
7,111,100
In case of withdrawal during the counting, the unit may not be consumed but the error remains limited to this single unit. We also see, in this example, that the last bit only changes 4 times, unlike the classic method where it changes 8 times. For this reason, it is thus possible to increase the number of units counted for the same number of erase write cycles. A capacity of 10,000 cycles corresponds to a maximum counting capacity of 40,000 units.

With this type of counter according to the invention, it is possible to achieve a greater memory capacity: a counter of n bits makes it possible to count up to 2n 32,000 units for 15 bits for example.

Several known types of coding offer the advantage of such a coding described. For some of them, for example for the one described in the table above (GRAY CODE), the increment (or decrement) algorithm is too simple. It can advantageously be implemented in the form of wired logic in the portable device, or in the form of a very simple program for a microprocessor.

This highlights another anti-fraud advantage of the invention: the management of the counter can be done in a secure manner. It is thus possible to design a portable device which knows only one order, the increment order; in this case, no direct access to the memory is possible. The reaction time of the device can thus be shortened.

It is also possible to give direct accesses to the memory, without losing this security advantage. It is thus possible to provide an instruction for reading the content of the counter. It is also possible to provide a recharging instruction, or more generally a direct write to the memory, conditioned by a security mechanism presentation of a secret recharging or personalization key, presentation of a "PIN code", etc.

It is also possible to provide the device with several meters of the proposed type.

This has several advantages. One can for example manage several counters each having a different monetary value. This makes it possible to debit at once (a single increment instruction) a large value or, on the contrary, a low value.

You can also manage several applications in the same portable object, to make a multi-service card for example.

A cost advantage is thus obtained (linked to the simplicity of the counting circuit) which is all the more important the greater the number of applications managed. In the latter case, it may be important that each application has its own protection. The various service providers who manage these applications do not need to share secrets (reload keys for example).

Claims (7)

1. Portable unit counting device in bits, with  an erasable and rewritable electronic memory  for storing said units characterized in that the  device also has a logic circuit which  counts units in a way that counting a  unit only involves a change of state of a  single bit and in that the count memory and the  logic increment (or decrement) circuit  are on a single electronic component. 2. Device according to claim 1, characterized in that  that the electronic component has a circuit  additional electronics that allow every bit  maybe written or erased individually. 3. Device according to claim 1, characterized in that  that the incremental logic circuit (or  decrement) is a programmable microprocessor. 4. Device according to one of the preceding claims,  characterized in that the portable device comprises  means that control that access to the function of  counting is only possible under conditions  a secret key or the identification of a  application. 5. Device according to one of the preceding claims,  characterized in that the device is provided with the means  who control that direct access to the meter, without  passing through the increment function (or  decrement) is made possible under certain conditions  a secret key or the identification of a  application. 6. Device according to one of the preceding claims,  characterized in that it has several counters. 7. Device according to claim 6, characterized in that  that the counters have different values.