Note: Descriptions are shown in the official language in which they were submitted.
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Rechargeable prepaid memory card
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns memory cards and, more
particularly, those used as a means of prepayment in
installations for the dispensing of products and/or
services.
2. Description of the Prior Art
A typical example of a memory card to which the
present invention can be applied is the prepaid phone
card which is purchased for a certain monetary value.
This value is memorized directly or indirectly in the
card and is decremented as and when it .is a sed. ~('he
invention, however, can also be used in other situations
where accounting units are recorded in the card and are
decremented or incremented as and when they are used.
These units may or may not have a monetary value. In the
rest of this description, we shall consistently use the
example of the prepaid telephone card for it is 'the most
eloquent example that could be used to explain the
advantages of the invention.
In a previous embodiment of a prepaid card, a
non-volatile electrically programmable and electrically
non-erasable memory is used as a means of storacle of the
prepaid value.
In this embodiment, the non-volative electrically
programmable memory (EPROM) contains P memory cells.
Each cell corresponds to an elementary accounting unit
of the commercial value. The cells are initially blank.
During use, a card reader associated with the dispensing
of products or services gives successive pulses for
programming the P cells one after the other, as and when
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the dispensing takes place. The residual value of the
card corresponds to the number of cells that have not
yet been programmed. When all the cells are programmed,
the prepaid credit is exhausted.
In another embodiment, the memory is electrically
erasable (EEPROM). Attention will be paid more
particularly to this latter example which more clearly
highlights the advantages of the invention. The memory
has P cells, each corresponding to an accounting unit.
There is furthermore provision for a counter, a register
containing a fixed number Z corresponding to a total
commercial value ZxP of the card expressed in accounting
units, and a comparator to compare the content of the
counter and that of the register. When the P cells of
the memory have been programmed, the counter is
incremented by one unit, and the cells are all erased
simultaneously, than again programmed successively, one
after the other. The content of the counter gets
incremented after each consumption of P accounting
units. When the content of the counter reaches the value
specified in the register, the comparator delivers a no
more credit signal which prevents the continued use of
the card. Thus, through the fact that the card is
electrically erasable, a card is made having a credited
value of ZxP although the memory has only P cells.
Of course, the counter is incremented by a circuit
internal to the card. It is not accessible at the
external terminals of the card as, in this case,
fraudulent activity would become possible.
In practice, it is possible to conceive of cards
containing, for example, a 50-cell memory (P = 50), arid
cards of 50, 100, 150, etc. accounting units could be
commercialised.
The erasable character of the memory is used to
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preserve a limited number of memory cells (P cells). At
the same time, broad possibilities of choice will be
retained as regards the commercial value of the card
(PxZ). The manufacturer of the integrated circuit will
have only one circuit to design, and all he has to do to
assign one commercial value or another to the card is to
use program the content of a register (in practice a
read-only memory) defining the number Z.
The present invention proposes mainly to use the
erasable character of the memory to make the card
rechargeable, i.e. so that the user who has exhausted
his credit can purchase an additional quantity of
accounting units without changing the card.
Another aim of the present invention is that when
the card contains only a small number of accounting
units, these units should not be lost to the user, even
when he recharges the card.
SI1MMARY OF TFIE INVENTION
According to the invention, there is proposed a
memory card serving as a means for the counting of
units, organized to count up to NxP units organized in N
pages of P units each, the card having a memory zone,
each cell of which represents an accounting unit, the
programming of this cell in a given state representing
the counting of a unit, the card having a page counter
and an incrementation circuit internal to the card to
increment the page counter by one unit after each
complete programming of the P cells of a page, said card
having an instructed value counter or credit counter,
the content of which represents a 'total value of Z pages
of units, and a comparator to emit a no more credit
signal when the page counter indicates that Z pages have
bean used up, the instructed value counter being
arranged so as to be incremented from outside the card.
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Instead of. the manufacturer's having to fabricate
different cards depending' on their commercial value,
only one card could be fabricated, and it is by the
initial r_harging and the subsequent rechargings of the
card that the credit value will be recorded in the card.
This approach can be applied chiefly if the memory
is electrically erasable. It is here that the invention
assumes all its value for it makes utmost use of the
erasable character of the memory. However, the approach
can be applied also if the memory is not erasable, in
which case the memory zone contains N pages of P cells.
The page counter is incremented whenever a full page is
used up, and the recharging operations consist in
incrementing the instructed value counter to increase
the number of pages of P cells which can be programmed,
the limit o.f the successive incrementations being
reached when 'the content of the instructed value counter
reaches the value N.
In the most worthwhile example of an erasable
memory, the memory zone contains P cells, i.e. it
corresponds to only one page of accounting units. When
the P cells of the card have been programmed, a page
counter incrementation signal is delivered (this signal
is set up within the card), and the P cells are erased.
The successive programming of the P cells can then start
again. When the content of the page counter reaches that
of the instructed value counter, a no more credit signal
is emitted, invalidating the subsequent functioning of
the card and prohibiting, for example, the erasure of
the P cells.
The card may then be recharged by incrementation of
the instructed value counter, within the limits of its
counting capacity. However, the card can also be
recharged before the no more credit signal is emitted.
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If there are remaining accounting units available in the
memory, they will not be lost since the recharging acts
on the instructed value counter and not on the
programming of the memory cells.
Preferably, the page counter and also the
instructed value counter are strictly irreversible, i.e.
not only do they count in only one direction, but they
also do not return to zero when they have reached their
maximum counting capacity.
Given that the instructed value counter is
accessible from the external connection terminals of the
card, it is highly desirable, and sometimes
indispensable, to provide for security of access to this
counter to prevent fraudulent activity. The invention
proposes a system for the use of cards with a
particularly simple security system, i.n the form of two
registers in the card. The first register, which is the
identification register, contains an identification
number of the card, for example a serial number recorded
at the very outset in the card. This number is
accessible in reading mode but, in principle, its
content cannot be modified. The register may be formed
with a read-only memory or an electrically programmable
memory with floating gate. The second register contains
a validation code which is the result of a computation
algorithm bringing into play both the content of the
first register and the content of the instructed value
counter. The validation code is computed by the card
recharging machine which reads the serial number of the
card, reads or knows the new content of the instructed
value counter and writes the result of the algorithm in
the Form of a validation code in the second register.
The validation code is verified in the card reader when
the card is used : The reader reads the serial number,
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the content of the credit counter and the content of the
validation register. It ascertains that there is
compatibility among these three contents, taking into
account the encoding algorithm used.
Among the advantages of the invention, it will be
noted that the card is compatible with the
non-rechargeable cards such as those described above: it
will be easy to see to it that the future applications
work with rechargeable or non-.rechargeable cards,
without distinction.
BRIEF DESCRIPTION OF THE DRAWING
Other characteristics and advantages of the
invention will appear from the following description,
made with reference to the appended drawing wherein the
single figure gives a schematic view of the integrated
circuit of the memory card according to the invention.
DESCRTPTTON OF A PREFERRED EMBODTMENT
The figure shows the architecture of the integrated
circuit of the rechargeable memory card according to the
invention. This figure shows only the parts specifically
concerned by the invention. It notably does not show the
circuits handling the transmissions of signals between
the card and 'the card reader or between the card and the
machine for recharging accounting units.
It shall be noted furthermore 'that various signal
input or output terminals have been shown in the figure.
However, certain terminals shown as being terminals that
are physically or electrically separated could be
brought together in the practical embodiment. For, it is
important to reduce the number of input/output terminals
of the card to the minimum, and there is frequently
provision for multiplexings of different signals at
common terminals to achieve this goal.
The example of the figure corresponds to a
rechargeable prepaid telephone card, using an
electrically erasable and electrically programmable
memory (EEPROM).
The integrated circuit has an EEPROM zone
designated by the reference MEM. This zone has P cells,
each corresponding to an accounting unit. The memory may
be constituted in matrix form with row and/or column
addressing decoders or, again, in the form of registers,
for example shift registers etc.
The figure shows a terminal DB providing access to
the card. Debitting pulses arrive through this terminal.
When the card is used in a public telephone booth, these
pulses come from the telephone line itself. Each pulse
has the effect of programming a cell of the memory MEM,
and the address of the cell to be programmed is
incremented, at each pulse, so that all the cells of the
memory which have not yet been programmed are programmed
successively. Programming circuits for prepayment cards
are known and shall not be described in greater detail.
The figure simply indicates the presence of a PGC
programming circuit between the terminal DB and the
memory MEM.
A circuit DET for detecting the end of programming
of the memory MEM is provided for. This circuit gives a
signal when the last cell (pth cell) is programmed. A
circuit EFF for the total erasure of the memory MEM is
also provided for. It erases the P cells of the memory
when it receives the order to do so from the circuit for
detecting the end of programming of a complete page of P
units.
The figure also shows two counters CPP and CPC and
a comparator COMP to compare the contents of the two
counters.
The counters are irreversible: they count in only
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one direction (for example incrementation only), and
they do not return to zero or to a prior content when
they have reached their maximum capacity. They can count
in binary mode or in BCD mode or in any other mode.
The first counter, CPP, is the counter of pages of
accounting units that have been used up. It is
incremented by the detection circuit DET (namely by a
circuit internal to the card) after each programming of
a full page of accounting units.
The second counter CPC is the instructed value
counter or credit counter. Its content is charged from
outside the card, more precisely by a credit recharging
machine. This is why a link has been shown between the
credit counter CPC and an external recharging terminal
CR. As stated above, this terminal has been shown as an
autonomous one, but it could be the same as another one,
for example the terminal DB, since the recharging of
credit will not be done during use in a telephone booth.
It may be assumed that the initial content charged
or loaded in the counter CPC is equal to Z. This is the
content when the unit leaves the factory or after an
initial passage through a credit recharging machine. The
initial content of the page counter CPP is equal to
zero. When the card is being used, the cells of the
memory MEM will be programmed tine by one as a function
of the consumption of telephone units (determined by the
reception of the debuting pulses at the terminal DB).
When the P cells have been programmed, the counter CPP
is incremented by one unit and the memory is completely
erased, and so on until the page counter CPP reaches the
value Z recorded in the instructed value counter CPC.
The comparator COMP then emits a no more credit signal
on an external terminal ST of the card. This signal
stops, for example, the telephone call or performs any
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other action, including action on the internal
functioning of the card. In particular, it may inhibit
the erasure of the memory which ought to take place when
the counter CPP reaches the value Z.
If the card is then introduced into a credit
recharging machine, this machine may increment the
counter by M units, for example up to a value of Y=Z+M.
The user pays for this incrementation, for example
proportionately to this incrementation, or by a sliding
scale tariff. He then has a fresh credit available of
(Y-Z)P accounting units. The working of the card is then
exactly the same as above.
The card is no longer rechargeable when the
instructed value counter has reached its maximum
capacity N.
The card can be recharged, as was stated, even when
the credit has not been exhausted, for example when the
page counter shows a content Z' smaller than the content
of the instructed value counter and when only a part P'
of the P cells of the memory has been programmed. The
remaining credit (Z-Z'-1)P + P-P' remains usable, and
the card recharged up to an instructed value Y includes
an overall credit (Y-Z')P-P' irrespectively of Z' and
P'.
The figure again shows two registers used to
provide for the security of the rechargings of the card
should the integrated circuit of the card be a simple
wired logic circuit using no microprocessor that could
provide fox this security system.
The first register RID is an identification
register for identifying the card. It may include, for
example, a serial number of the card, or a batch number
or any fixed node number. The more the identification
code is proper to the card, the greater is the extent to
to
which the security is ensured. In other words, the
security level is very high if two separate cards have
practically no chance of having the same code. This
first register RID is, for example, made in the form of
a read-only memory (ROM) or an electrically programmable
register with floating gate. It is accessible in reading
made from an external terminal ID so that the card
reader being used or the credit recharging machine can
read the code that it contains.
The second register RVL is a validation register.
It contains a validation code making it possible to
ascertain that there has been no fraudulent activity. It
is accessible in reading mode by the card reader or the
credit recharging machine. Tt is accessible in writing
mode by the credit recharging machine alone. An external
access terminal VL has been shown. An external access
terminal VL has been shown. This could be the same
terminal as the terminal ID with an appropriate
multiplexing of signals. The register is constituted by
an electrically erasable and reprogrammable memory.
The following is the method of validation: when the
card is being recharged, the recharging machine reads
the content Z of the instructed value counter. It
increments the counter until the new instructed value Y
desired. Starting from the new content and from the
identification code read in the register RID, it
establishes a validation code according to a
well-defined algorithm. This code is recorded in the
validation register RVL.
During use in a card reader associated with a
services dispensing machine (telephone booth), the
reader starts by reading the content of the instructed
value counter and of the identification and validation
registers at the terminals CR, ID, VL. It ascertains
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that these contents are compatible, taking into account
the algorithm used by the recharging machine. For
example, it redoes the reverse algorithm on the basis of
the content of 'the validation register or it redoes the
same algorithm as the recharging machine and ascertains
that the result of the computation coincides ~,rith the
content of the validation register RVL.
If there is no compatibility among the contents of
the two registers and of the counter, the card reader
prohibits the dispensing of services or products
requested by the user. It can also prevent the card from
being restored to the user.
The checking of the validation register does not
necessarily imply the execution of the starting
algorithm or of the reverse algorithm. In certain cases,
i.t may be restricted to a briefer checking of parity
computations etc.
The identification and validation codes are not
necessarily contained in registers directly connected to
external terminals of the integrated circuit. They may
be contained in specific zones of the memory MEM, these
zones being accessible through an address decoder. The
checking of the card then requires an addressing of
these specific zones of the memory MEM since it is these
zones that have the function of the validation register
RVL and identification register RID.
The invention makes it possible, notably, to easily
make high-capacity telephone cards for people who much
need to use public phone booths for long-distance calls.
