IC card

Abstract: There is provided a command input type IC card including a plurality of memory semiconductor elements capable of electrically writing and batch-erasing, and an address decoder for decoding a card enable signal on the basis of an address signal so as to selectively output a chip enable signal to one of the memory semiconductor elements. The operating modes of each element are determined on the basis of a command input from the outside. The IC card also includes a command detector and a latch circuit, both of which inhibit the address decoder from a decoding operation when the command input from the outside is a predetermined command. The card enable signal is thereby supplied as the chip enable signal to all the memory semiconductor elements.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION: The present invention relates to an IC card and, more particularly, to a command input type IC card having a plurality of built-in memory semiconductor elements capable of electrically writing and batch-erasing. DESCRIPTION OF THE RELATED ART: Fig. 2 is a block diagram showing the structure of the circuitry on a conventional command input type IC card. Two memory semiconductor elements 2 and 3, having similar structures, are connected to an address decoder 1. Each of the memory semiconductor elements 2 and 3 is a command input type element that inputs commands from the outside to determine operating modes on the basis of the commands, and is capable of electrically writing and batch-erasing. A card enable signal line 6 and a signal line 7a, one of the signal lines running through an address bus 7, are connected to the address decoder 1. The address bus 7, a read enable signal line 8, a write enable signal line 9, a data bus 10 and a program power supply line 11 are all connected to both of the memory semiconductor elements 2 and 3. The memory semiconductor element 2 is connected to the address decoder 1 by a chip enable signal line 12; similarly, the memory semiconductor element 3 is connected to the address decoder 1 by another chip enable signal line 13. The card enable signal line 6, the read enable signal line 8 and the write enable signal line 9 are pulled-up to power sources by resistors 16, 17 and 18, respectively. Fig. 3 shows the inner structure of the memory semiconductor element 2. The address bus 7 is connected to a memory cell array 20 through an X address decoder 21 and a Y address decoder 22. The data bus 10 is connected to the memory cell array 20 through a data input output circuit 24 (a data I/O circuit 24). A command latch circuit 25 is connected to the data bus 10. A control logic circuit 23 is connected to the X address decoder 21, the Y address decoder 22, the data I/O circuit 24 and the command latch circuit 25. The chip enable signal line 12, the read enable signal line 8, the write enable signal line 9 and the program power supply line 11 are all connected to the control logic circuit 23. When data is read from the memory semiconductor element 2, the level of the chip enable signal line 12 and that of the read enable signal line 8 are both made low, whereas the level of the write enable signal line 9 is made high. At the same time, an ordinary supply voltage is applied to the program power supply line 11. When a desired address is specified on the address bus 7, the X and Y address decoders 21 and 22 select a memory cell corresponding to the specified address from the memory cell array 20. Data stored in this memory cell is output to the data bus 10 via the data I/O circuit 24. When data is written or batch-erased, a program voltage is applied to the program power supply line 11, and the level of the read enable signal line 8 is made high, whereas the level of the chip enable signal line 12 and that of the write enable signal line 9 are both made low. Under these conditions, when a command is input through the data bus 10, it is retained by the command latch circuit 25. Whether the data is written or batch-erased depends on the contents of this command. When data is written, the level of the chip enable signal line 12 and that of the write enable signal line 9 are both made low, and the level of the read enable signal line 8 is made high. The data is input to the data bus 10 and is thereby written into a desired address. The level of the chip enable signal line 12 and that of the read enable signal line 8 are both made low, whereas the level of the write enable signal line 9 is made high. The written data is read on the data bus 10 and is verified by a predetermined algorithm. When data is batch-erased, in the same manner as in writing, the level of the chip enable signal line 12 and that of the write enable signal line 9 are both made low, whereas the level of the read enable signal line 8 is made high. After the contents of all the memory cells in the memory array 20 have been erased, the level of the chip enable signal line 12 and that of the read enable signal line 8 are both made low, whereas the level of the write enable signal line 9 is made high. An algorithm different from that used in writing verifies batch erasure. When the level of the chip enable signal line 12 is high, the memory semiconductor element 2 becomes inactive and does not perform any operation, regardless of the levels of the other signal lines. In this way, to actuate the IC card, shown in Fig. 2, having the built-in memory semiconductor elements 2 and 3, a predetermined voltage is applied to the program power supply line 11, and the level of the card enable signal line 6 is made low. A card enable signal is decoded on the basis of a part of an address signal which is input to the address decoder 1 through the signal line 7a. As a result, an L-level chip enable signal is output from the address decoder 1 to one of the memory semiconductor elements 2 and 3 in accordance with an address specified by the address signal. The memory semiconductor element having received the chip enable signal becomes active, thus making it possible to perform various operations mentioned above. The address decoder 1 makes the level of one chip enable signal line 12, connected to the memory semiconductor element 2, high, and also makes the level of the other chip enable signal line 13, connected to the memory semiconductor element 3, low, or vice versa. Therefore, when the contents stored in all the memory semiconductor elements 2 and 3 in the entire IC card are erased, the contents should be erased element by element. Thus the contents stored in the memory elements of the IC card cannot be simultaneously batcherased. For this reason, it takes an enormous amount of time and labor to erase the contents stored in the entire IC card. JP 3065745 discloses an IC card which enables the change of a data bus width by enabling different numbers of memories. When a data bus having 32 bits is desired to be formed, the decoding operation is inhibited so that all memories are simultaneously selected. The device is not directed to the achievement of batch erasure. SUMMARY OF THE INVENTION The present invention has been accomplished to solve the above described disadvantages. Accordingly, the object of the invention is to provide an IC card capable of batch-erasing the contents stored in all built-in memory semiconductor elements. In order to achieve the above object, according to this invention, there is provided an IC card as set out in claim 1. Preferred features of the invention are set out in claims 2 and 3. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the structure of the circuitry on an IC card in accordance with an embodiment of the present invention; Fig. 2 is a block diagram showing the structure of the circuitry on the conventional IC card; and Fig. 3 is a circuit diagram showing the inner structure of a memory semiconductor element used in this invention. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the accompanying drawings. Fig. 1 is a block diagram showing the structure of the circuitry on an IC card in accordance with the embodiment of this invention. Two memory semiconductor elements 2 and 3, having similar structures, are connected to an address decoder 31. Each of the memory semiconductor elements 2 and 3 is a command input type element that inputs commands from the outside to determine operating modes on the basis of the commands, and is capable of electrically writing and batch-erasing. A card enable signal line 6, a read enable signal line 8, and a signal line 7a, one of the signal lines running through an address bus 7, are all connected to the address decoder 31. The address bus 7, the read enable signal line 8, a write enable signal line 9, a data bus 10 and a program power supply line 11 are all connected to both of the memory semiconductor elements 2 and 3. The memory semiconductor element 2 is connected to the address decoder 31 by a chip enable signal line 12; similarly, the memory semiconductor element 3 is connected to the address decoder 31 by another chip enable signal line 13. The card enable signal line 6, the read enable signal line 8 and the write enable signal line 9 are pulled-up to power sources by resistors 16, 17 and 18, respectively. The IC card has a command decoder 4 to which the card enable signal line 6, the write enable signal line 9, the data bus 10 and the power supply line 11 are all connected The output 14 of the command decoder 4 is connected to a latch circuit 5, whose output 15 is connected in turn to the address decoder 31. The write enable signal line 9 is connected to the latch circuit 5. The command decoder 4 and the latch circuit 5 constitute a means for inhibiting decoding. The memory semiconductor elements 2 and 3 each have an inner structure similar to that shown in Fig. 3. The command decoder 4 decodes data input to the data bus 10 when the level of the card enable signal line 6 and that of the write enable signal line 9 are both low and when a program voltage is applied to the program voltage line 11. The command decoder 4 makes the level of the output 14 high when the decoded data contains a specific code indicating batch erasure. The latch circuit 5 latches the output of the command decoder 4 at the leading edge of the write enable signal line 9, and transmits this output. The address decoder 31 enters an ordinarily operating mode not only when the level of the output 15 of the latch circuit 5 is low, but also when the level of the output 15 is high and that of the read enable signal line 8 is low. The address decoder 31 then selects either of the memory semiconductor elements 2 or 3 on the basis of address signals input through the signal line 7a. It outputs a card enable signal, which is input through the card enable signal line 6, to the chip enable signal line 12 or 13 as a chip enable signal. On the other hand, when the level of the output 15 of the latch circuit 5 and that of the read enable signal line 8 are both high, the address decoder 31 directly outputs the card enable signal to both of the chip enable signal lines 12 and 13 as a chip enable signal, regardless of the address signals. In other words, at this time the address decoder 31 is inhibited from its decoding operation. The operation of the IC card will now be described. To perform reading or writing, a read or a write command is input through the data bus 10. The command decoder 4 will not make the level of output 14 high with respect to the read or write command. In other words, since the level of the output 15 of the latch circuit 5 remains low, the address decoder 31 is in the ordinary operating mode and selects either of the memory semiconductor elements 2 or 3 on the basis of the address signal. Thus the IC card is capable of performing reading as well as writing in the same manner as the conventional IC card, shown in Fig. 2. To perform batch erasure, the program voltage is applied to the program power supply line 11, and at the same time, the level of the card enable signal line 6 and that of the write enable signal line 9 are both made low, whereas the level of the read enable signal line 8 is made high. Under these conditions, data containing the specific code that indicates batch erasure is input through the data bus 10. As a result, the command decoder 4 makes the level of output 14 high, thus inputting an H-level signal to the address decoder 31 via the latch circuit 5. At this stage, because the level of the read enable signal line 8 is also high, the address decoder 31 enters a decode inhibiting mode, thus outputting an L-level chip enable signal to both of the chip enable signal lines 12 and 13. The memory semiconductor elements 2 and 3 both become active, thereby simultaneously batch-erasing the contents stored in the memory semiconductor elements 2 and 3. Then, the level of the card enable signal line 6 and that of the read enable signal line 8 are both made low, whereas the level of the write enable signal line 9 is made high. The batch erasure is verified. At this stage, because the level of the output 15 of the latch circuit 5 remains high, the address decoder 31 enters the ordinary operating mode, and selects either of the memory semiconductor elements 2 or 3 on the basis of the address signal. The batch erasure can thus be verified normally. In the above embodiment, although an IC card having the two built-in memory semiconductor elements 2 and 3 has been described, the same advantages as those described above are obtainable with an IC card having three or more built-in memory semiconductor elements. Though the memory semiconductor elements 2 and 3 use two types of supply voltages, a normal supply voltage and a program voltage, a memory semiconductor element operated on a single power supply may also be employed so long as this element is a type whose operating modes are determined by command input. The operating mode of the memory semiconductor element is not limited to reading, writing and batch-erasing modes, but may include other modes such as a partial-erasing mode.

Claims: An IC card comprising: a plurality of semiconductor memory elements (2, 3), whose operating modes are determined on the basis of a command input from the outside, said semiconductor memory elements being capable of electrically writing and batch-erasing; an address decoder (31) for decoding a card enable signal ( CE ) on the basis of an address signal (7a) so as to selectively output a chip enable signal (12 or 13) to one of the plurality of semiconductor memory elements (2, 3); and decode inhibiting means (4, 5) for inhibiting said address decoder (31) from performing a decoding operation; characterised in that the decode inhibiting means includes a command decoder (4) which decodes data input to a data bus (Dm) and outputs a decode inhibiting signal (14) when the decoded data contains a specific code indicating batch erasure, the address decoder (31) supplies the card enable signal as the chip enable signal (12,13) to all the semiconductor memory elements (2, 3) when it receives the decode inhibiting signal (14) from the command decoder (4) and a read enable signal line is not in an active state. An IC card as claimed in claim 1 comprising a latch circuit (5) which latches the decode inhibiting signal (14) from the command decoder (4) and outputs it to a decode inhibiting signal input terminal of said address decoder (31). An IC card as claimed in claim 2 wherein said latch circuit (5) latches the output of said command decoder (4) at a leading edge of a write enable signal.

Inventors: SANEMITSU YOSHIKADO, SANEMITSU, YOSHIKADO, Sanemitsu, Yoshikado, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: G06K19
IPC codes: G06K19, G11C11, G11C16, G07F7