I.C. card

Abstract: An IC card comprises a first semiconductor memory such as a 256 K bits RAM (1) for storing main data, a second semiconductor memory such as 64 K bits EEPROM (2) for storing physical information concerning the IC card, e.g., size, capacity and access time, a control circuit (3) for selectively enabling one of the first and second semiconductor memories to operate, an address BUS (5) connected to the first and second semiconductor memories, a data BUS (7) connected to the first and second semiconductor memories, and a decoder (4) for decoding a write control signal (WE) for the second semiconductor memory using part of the address signal necessary for making access to the second semiconductor memory and delivering the decoded write control signal to the second semiconductor memory. Consequently, the area in the second semiconductor memory is divided into a non-rewritable region which does not permit rewrite of the data and a writable region which permits rewrite of the data.

Description: The present invention relates to an IC card and, more particularly, to an IC card which has, in addition to a semiconductor memory for storing the main data, a semiconductor memory for storing physical information concerning the card and format information concerning the data in the card. DESCRIPTION OF THE RELATED ART: Fig. 4 shows an IC card of the type described above. The IC card has a 256 K bit static RAM 1 serving as an area for storing main data, and a 64 K bit EEPROM 2 which is adapted to store physical information concerning the IC card, e.g., type and capacity of the memory, access time and so on, as well as format information concerning the data stored in the IC card. A mode control circuit 3 is connected to the static RAM 1 and the EEPROM 2. In addition, all the address signal lines A₀ to A₁₄ of an address BUS 5 are connected to the static RAM 1. Selected address signal lines A₀ to A₁₂ of the BUS are also connected to the EEPROM 2. Furthermore, a data BUS 7 including 8-bit data signal lines D₀ to D₇ is connected to the static RAM 1 and also to the EEPROM 2. The mode control circuit 3 receives a card enable signal CE and a memory selection signal REG . A chip enable signal S₁ of "L" level is delivered to the static RAM 1 when the card enable signal CE is "L" while the memory selection signal REG is of "H" level. When both the card enable signal CE and the memory selection signal REG are of "L" level, a chip enable signal S₂ of "L" level is delivered to the EEPROM 2. The operation of this IC card is as follows. When it is desired to use the static RAM 1, a terminal device which is not shown sets the card enable signal CE to "L" level and sets the memory selection signal REG to "H" level. As a result, a chip enable signal S₁ of "L" level is delivered from the mode control circuit 3 to the static RAM 1 so that the static RAM 1 becomes ready to operate. In this state, an address is appointed through the address signal lines A₀ to A₁₄, and read control signal OE and write control signal WE are respectively set to "L" and "H" levels, so that data stored in the appointed address of the RAM 1 appears on the data BUS 7. Conversely, when the read control signal OE and the write control signal WE are respectively set to "H" and "L" levels, data on the data BUS 7 are written in the appointed address of the static RAM 1. The data in the static RAM 1 is extinguished when the power supply is turned off. On the other hand, when the EEPROM 2 is to be used, both the card enable signal CE and the memory selection signal REG are set to "L" levels. As a result, a chip enable signal S₂ of "L" level is delivered to the EEPROM 2 from the mode control circuit 3, thereby enabling the EEPROM 2 to operate. Reading and writing of data are conducted in the same manner as those in the case of the static RAM 1. The data in the EEPROM 2 is not extinguished even when the power supply is turned off. When both the static RAM 1 and the EEPROM 2 are not to be used, the card enable signal CE is set to "H" level. In this case, both the chip enable signals S₁ and S₂ are set to "H" so that the static RAM 1 and the EEPROM 2 become inoperative. In this known IC card, the EEPROM 2 can be accessed easily through a terminal device (not shown) as described above, so that a problem has been encountered that the physical information concerning the card stored in the EEPROM 2 may be rewritten accidentally or willfully. Generally, unauthorised memory access can be prevented by hardware and/or software control means inhibiting access to a given range of addresses in the memory, cf. e.g. EP-A-0 331 407 disclosing an inhibition address checker. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an IC card which prevents physical information stored therein from being easily rewritten through a terminal device. To this end, according to the present invention, there is provided an IC card comprising: a first semiconductor memory for storing data; a second semiconductor memory for storing physical information concerning the IC card; a control circuit for selectively enabling one of said first and second semiconductor memories to operate, said second semiconductor memory being non-volatile; an address BUS connected to said first and second semiconductor memories; and a data BUS connected to said first and second semiconductor memories; characterised by a decoder for decoding a write control signal for said second semiconductor memory using part of the address signal necessary for making access to said second semiconductor memory and delivering the decoded write control signal to said second semiconductor memory; wherein said address BUS has a plurality of signal lines corresponding to a plurality of bits, said decoder is operative for selectively decoding said write control signal for said second semiconductor memory in accordance with the levels of at least one of said plurality of signal lines whereby said second semiconductor memory has a rewritable memory region and a non-rewritable memory region. In the present invention, the decoder decodes the write control signal for the second semiconductor memory by using part of the address signal which is necessary for making access to the second semiconductor memory, whereby a part of the second semiconductor memory is changed into a non-writable area. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of an IC card in accordance with an embodiment of the present invention; Fig. 2 is an illustration of the operation of a decoder 4 incorporated in the embodiment shown in Fig. 1; Fig. 3 is an illustration showing an arrangement of memories in EEPROM; and Fig. 4 is a block diagram of a conventional IC card. DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the accompanying drawings. Referring to Fig. 1, an IC card embodying the present invention has a 256 K bits static RAM 1 which provides an area for storing main data, and a 64 K bits EEPROM 2 adapted for storing physical information concerning the IC card, e.g., type and capacity of the memory, access time and so on, as well as format information concerning data stored in the IC card. A mode control circuit 3 is connected both to the static RAM 1 and the EEPROM 2. All the address signal lines A₀ to A₁₄ of an address BUS 5 are connected to the static RAM 1, and selected address lines A₀ to A₁₂ are also connected to the EEPROM 2. A data BUS 7 formed of 8-bit signal lines D₀ to D₇ is connected both to the static RAM 1 and the EEPROM 2. The mode control circuit 3 receives a card enable signal CE and a memory selection signal REG. When the card enable signal CE is of "L" level while the memory selection signal REG is of "H" level, the mode control circuit 3 delivers a chip enable signal S₁ of "L" level to the static RAM 1, whereas, when both the card enable signal CE and the memory selection signal REG are of "L" level, the mode control circuit 3 delivers a chip enable signal S₂ of "L" level to the EEPROM 2. A decoder 4 is connected to a write control input terminal 2a of the EEPROM 2. Two signal lines A₁₁ and A₁₂ out of the address BUS 5 are connected to the decoder 4. The decoder 4 decodes a write control signal WE in accordance with the levels of the signal lines A₁₁ and A₁₂, and delivers to the EEPROM 2 a new write control signal WED shown in Fig. 2. More specifically, when both the signal lines A₁₁ and A₁₂ are of "L" level, the decoder 4 decodes the write control signal WE of "L" level to a write control signal WED of "H" level, thereby prohibiting writing in the EEPROM 2. The write control signal WE is directly supplied to a write control input terminal 1a of the static RAM 1. A read control signal OE is input both to the read control signal input terminals 1b and 2b of the static RAM 1 and the EEPROM 2. In the described embodiment, the static RAM 1 serves as the first semiconductor memory, while the EEPROM 2 serves as the second semiconductor memory. The operation of this embodiment is as follows. When it is desired to use the static RAM 1, a terminal device (not shown) sets the card enable signal CE to "L" level, while setting the memory selection signal REG to "H" level. Consequently, the mode control circuit 3 delivers a chip enable signal S₁ of "L" level to the static RAM 1, thus enabling the static RAM 1 to operate. In this state, when the desired address is appointed through the address signal lines A₀ to A₁₄ of the address BUS 5, while the read control signal OE and the write control signal WE are respectively set to "L" and "H" levels, the data in the appointed address of the static RAM 1 appears on the data BUS 7. Conversely, when the read control signal OE and the write control signal WE are respectively set to "H" and "L" levels, the data on the data BUS 7 are written in the appointed address of the static RAM 1. The data in the static RAM 1 is extinguished when the power is turned off. On the other hand, when the EEPROM 2 is to be used, both the card enable signal CE and the memory selection signal REG are set to "L" level. Consequently, a chip enable signal S₂ of "L" level is delivered from the mode control circuit 3 to the EEPROM 2, thus enabling the EEPROM 2 to operate. The operation for reading data from the EEPROM 2 is conducted in the same manner as that in the case of the static RAM 1. Namely, the data stored in the address of the EEPROM 2 appointed through the address signal lines A₀ to A₁₂ of the address BUS 5 appears on the data BUS 7 when the read control signal OE and the write control signal WE are respectively set to "L" and "H". For writing data in the EEPROM 2, the address in which the data is to be written is appointed through the address signal lines A₀ to A₁₂ of the address BUS 5, and the read control signal OE and the write control signal WE are respectively set to "H" and "L" levels. The write control signal WE is input to the decoder 4 so as to be decoded in accordance with the levels of the signal lines A₁₁ and A₁₂ connected to the decoder 4. As will be seen from Fig. 2, in the cases other than the case where both the signal lines A₁₁ and A₁₂ are of "L" level, i.e., when one of the addresses 800 to 1FFF by hexadecimal notation has been appointed, the write control signal WE of "L" level is input to the EEPROM 2 as a new write control signal WED while maintaining the level "L". Consequently, the data on the data BUS 7 is written in the appointed address of the EEPROM 2. Conversely, when both the signal lines A₁₁ and A₁₂ are of "L" level, i.e., when one of addresses 0 to 7FF by hexadecimal notation has been appointed, the write control signal WE of the "L" level is decoded into a new write control signal WED of "H" level, and this new write control signal WED is input to the EEPROM 2, so that the writing of data in the EEPROM 2 is prohibited. Thus, in the described embodiment, as shown in Fig. 3, the area of the addresses 0 to 7FF of the EEPROM 2 forms a non-rewritable region R1, while the area of addresses 800 to 1FFF forms a rewritable region R2. Therefore, the physical information concerning the IC card, which should not be rewritten easily, is stored in this non-rewritable region R1, while other information such as format information of the data is stored in the rewritable region R2. The physical information concerning the card, stored in the memory region R1, cannot easily be rewritten through the terminal device. The data in the EEPROM 2 is not extinguished even when the power is turned off. When both the static RAM 1 and EEPROM 2 are not to be used, the card enable signal CE input to the mode control circuit 3 is set to "H" level. In this case, the chip enable signals S₁ and S₂ are set to "H" level regardless of the level of the memory selection signal REG , so that both the static RAM 1 and the EEPROM 2 become inoperative. Although a 256 K bit static RAM 1 is used as the first semiconductor memory in the described embodiment, this is not exclusive and semiconductor memories of different types and capacities can be used equally well. It is also to be understood that the 64 K bit EEPROM 2 can be substituted by other suitable writable semiconductor memory. The described decoding method performed by the decoder 4 also is illustrative and the same effect can be obtained also when other decoding methods are used. As will be understood from the foregoing description, in the IC card of the present invention, the physical information concerning the IC card is not easily rewritable through a terminal device, so that the reliability of the IC card can be greatly improved.

Claims: An IC to card comprising: a first semiconductor memory (1) for storing data; a second semiconductor memory (2) for storing physical information concerning the IC card; a control circuit (3) for selectively enabling one of said first and second semiconductor memories to operate, said second semiconductor memory being non-volatile; an address BUS (5) connected to said first and second semiconductor memories; and a data BUS (7) connected to said first and second semiconductor memories; characterised by a decoder (4) for decoding a write control signal ( WE ) for said second semiconductor memory using only a part of the address signal necessary for making access to said second semiconductor memory and delivering the decoded write control signal (WED) to said second semiconductor memory; wherein said address BUS (5) has a plurality of signal lines (A0 ∼ A14) corresponding to a plurality of bits, said decoder (4) is operative for selectively decoding said write control signal ( WE ) for said second semiconductor memory (2) in accordance with the levels of at least one of said plurality of signal lines whereby said second semiconductor memory has a rewritable memory region (R2) and a non-rewritable memory region (R1). An IC card according to claim 1, wherein said non-rewritable memory region stores said physical information concerning the IC card. An IC card according to claim 1, wherein said second semiconductor memory has a PROM.

Inventors: YOSHIKADO SANEMITSU, YOSHIKADO, SANEMITSU,, Yoshikado, Sanemitsu, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: G07F7
IPC codes: G07F7, G06K19, B42D15, G11C5