JPH04220789A - Clock switching method for ic card - Google Patents

Abstract

PURPOSE:To change over from an internal clock pulse to an external clock pulse after checking that the external clock pulse is inputted as to the method of changing over the actuation clock to the external clock when it is connected to the device in an IC card integrating a built-in processor actuated with the internal clock. CONSTITUTION:In the IC card provided with an internal clock source 2 generating the internal clock pulse, a processor 1 actuated with the actuation clock, an input part 4 inputting data, a display part 5 displaying the data, a battery 6 for actuation and an external connection terminal 7, an external clock pulse detection circuit 8 detecting the external clock pulse is provided, the processor 1 checks the external clock pulse with the output of the external clock detection circuit 8 and changes over the actuation clock from the internal clock pulse to the external clock pulse.

Description

[Detailed description of the invention]

(Table of Contents) Industrial Application Fields Conventional Technology (FIG. 6) Problems to be Solved by the Invention Means for Solving Problems (FIG. 1) Functional Example (a) Description of an Embodiment (FIG. 2) 5) (b) Description of other embodiments Effects of the invention

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clock switching method for switching an operating clock to an external clock when connected to a device in an IC card incorporating a processor that operates using an internal clock.

[0003] In recent years, IC cards have become popular as cards that can store large amounts of data and are highly secure. In particular, IC cards with a built-in processor, display section, and input section are being used in various fields. is expected.

[0004] Such IC cards have an internal battery and can be used stand-alone (independently) and can be used for displaying, calculating, searching, etc. internal data, but the battery life is about 1 to 3 years. There is a strong demand for short and power saving.

[0005] For this reason, an easily available crystal oscillator of about 32 KHz is provided as an internal clock source inside the IC card.
When used standalone, the processor's operating clock speed is lowered to save power.

On the other hand, when operating within an IC card reader/writer, it is standardized that the IC card reader/writer supplies a clock and power of approximately 4 MHz, so a clock pulse switching technique is required. .

[0007]

2. Description of the Related Art FIG. 6 is an explanatory diagram of a conventional IC card.

In the figure, 1 is a processor that operates with an operating clock, 2 is an internal clock source that is composed of a crystal oscillator, and provides an internal clock pulse of about 32 KHz to the processor 1, and 3 is a memory. 4 is an input section, which is for storing data, and is composed of a key input section, and is for inputting data etc. to the processor 1. 5 is a display section, which displays the data of the processor 1. 6 is a battery that supplies internal voltage of about 3 volts to each part, 7 is an external terminal of the IC card,
It has external voltage (+5 volts) terminal, external clock pulse terminal, reset (RST) terminal, input/output (IO) terminal, ground terminal, etc. D1 and D2 are diodes, which prevent backflow of external voltage and battery voltage, respectively. It is for.

[0009] In such an IC card, the processor 1 operates on internal clock pulses from an internal clock source 2 when it is standalone, and switches to external clock pulses when it is set in an IC card reader/writer. ing.

[0010] Conventionally, this clock pulse switching has been performed by using a reset signal from a reset terminal of the IC card, or by detecting an external voltage from an external voltage terminal (Japanese Patent Laid-Open Publication No. 62-237592, etc.). there were.

[0011]

[Problems to be Solved by the Invention] However, the prior art has the following problems.

■The method using a reset signal has a reset terminal exposed on the surface of the IC card, and since it is a single pulse,
During stand-alone use, if a metal object such as a clip accidentally touches the reset terminal and a voltage equivalent to the reset signal is applied, the internal clock will switch to the external clock and clock pulses will no longer be supplied to the IC card. , it will not work and will be in the same state as a failure.

[0013] ■The method of detecting external voltage is that the external voltage terminal is exposed on the surface of the IC card, and during stand-alone use, static electricity, etc. flows to the external voltage terminal, and a voltage equivalent to the external voltage is applied. Then, the internal clock is temporarily switched to the external clock, and the processor's clock sequence cannot be followed, which can cause the processor to run out of control, become inoperable, and end up in the same state as a failure.

■ In both methods, the external clock pulse is
There is no guarantee that the external clock pulse is being input to the card, and if for some reason the external clock pulse is not input to the IC card, the IC card will become inoperable even if switching is performed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an IC card clock switching method that can switch from an internal clock pulse to an external clock pulse after confirming that an external clock pulse has been input.

[0016]

[Means for Solving the Problems] FIG. 1 is a diagram showing the principle of the present invention.

Claim 1 of the present invention provides an internal clock source 2 that generates internal clock pulses, a processor 1 that operates according to an operating clock, an input section 4 for inputting data, and a display section 5 for displaying data. and battery 6 for operation.
and an external connection terminal 7, an external clock detection circuit 8 for detecting an external clock pulse from the external connection terminal 7 is provided, and the output of the external clock detection circuit 8 causes the processor 1 to The method is characterized in that the operating clock is switched from the internal clock pulse to the external clock pulse after confirming the external clock pulse.

[0018] Claim 2 of the present invention provides the following in claim 1:
The external clock detection circuit 8 frequency-divides the external clock pulse, and the processor 1 identifies the external clock pulse from the frequency-divided output according to the internal clock pulse.

[0019] Claim 3 of the present invention provides the following in claim 1:
The processor 1 is characterized in that it switches the operating clock from the external clock pulse to the internal clock pulse in response to a termination command from the external connection terminal 7.

[0020]Claim 4 of the present invention provides the following in claim 1:
An external voltage detection circuit 9 is provided for detecting an external voltage from the external connection terminal 7, and the processor 1 detects that the external voltage is no longer applied, and changes the operating clock from the external clock pulse to the internal one. It is characterized by switching to a clock pulse.

[0021]

[Operation] According to claim 1 of the present invention, since the clock pulse is switched after confirming that an external clock pulse has been input, even if the external terminal contacts something, it will not become a clock pulse, and when used as a stand-alone. can prevent malfunction of
Switching is possible while an external clock pulse is input.

According to the second aspect of the present invention, the external clock detection circuit 8 is constituted by a frequency dividing circuit, so that it can be constituted by a digital circuit, and low voltage and LSI implementation are possible.

According to claim 3 of the present invention, since the external clock pulse is returned to the internal clock pulse by a command, the clock pulse can be returned without adding any special circuit.

In claim 4 of the present invention, since the external voltage is detected and the external clock pulse is returned to the internal clock pulse, the clock pulse can be returned and the clock can be switched without issuing a command from the IC card reader/writer. Since it is limited to one direction from the external clock to the internal clock, malfunctions due to static electricity etc. can be prevented when stand-alone.

[0025]

Embodiment (a) Description of an Embodiment FIG. 2 is an explanatory diagram of an IC card according to an embodiment of the present invention, and FIG. 3 is a block diagram of an IC card according to an embodiment of the present invention.

In the figures, the same parts as those shown in FIGS. 1 and 6 are indicated by the same symbols.

As shown in the front view of the IC card in FIG. 2(A), the surface of the IC card includes an IC card contact section 7 consisting of eight external terminals, a display section 5, a numeric keypad, a collation key, and a power supply. An input section 4 consisting of an on/off key is provided.

As shown in the cross-sectional view of the IC card in FIG. A battery 6 is provided below the plate 40.

In FIG. 3, the external clock detection circuit 8 is composed of 8 stages of series-connected flip-flops (FF), and has a frequency of about 4.1 MH from an external clock pulse terminal.
The frequency of the external clock pulse of z is divided by 8 to produce a frequency-divided output of 16 KHz, which is output to the processor 1. Voltage detection circuit 9
is a voltage dividing resistor R that divides the external voltage from the external voltage terminal.
1, R2, a capacitor C connected in parallel with the voltage dividing resistor R2, and a comparison amplifier AMP that compares an external voltage with the voltage of the capacitor C and outputs a reset signal.

FIG. 4 is a flowchart of a clock switching process according to an embodiment of the present invention, and FIG. 5 is an explanatory diagram of the operation of an embodiment of the present invention.

(2) When the IC card is set in the IC card reader/writer, a reset signal is output from the IC card reader/writer. In the IC card, when the processor 1 receives this reset signal from the reset terminal, the processor 1 switches from standalone mode to online mode.

■The processor 1 checks the frequency-divided output of the external clock detection circuit 8 using the internal clock (32 KHz), and as shown in FIG. 5(A), if there is a change in the frequency-divided output, it detects the external clock pulse. If there is no change, it is assumed that the external clock pulse is not detected.

[0033] If no external clock pulse is detected, processor 1 returns to standalone mode and ends.

(2) On the other hand, upon confirming the detection of the external clock pulse, the processor 1 switches the operating clock from the internal clock pulse to the external clock pulse. And I
The C card communicates with an IC card reader/writer.

■After the end of communication, when the IC card begins to be ejected from the IC card reader/writer, the external power supply voltage (5
volt) to battery voltage (3 volts). At this time, as shown in FIG. 5(B), the capacitor C of the power supply detection circuit 9 is discharged from the state charged to 3.5 volts by the power supply voltage, and the input voltage on the capacitor C side of the comparator amplifier AMP becomes The voltage becomes higher than the voltage at the external voltage terminal, and a low-level reset pulse is issued to the processor 1. As a result, the processor 1 detects the power off, returns the operating clock from the external clock pulse to the internal clock pulse, returns to the standalone mode, and the IC card is completely ejected.

In this way, the processor 1 detects that the external clock pulse has been reliably received and switches the internal clock pulse to the external clock pulse.

Therefore, even if something touches the external terminal during stand-alone operation, no malfunction will occur, and even if no external clock pulse is output due to a defect in the IC card reader/writer or a defective contact connection, no malfunction will occur.

Furthermore, since the external clock detection circuit 8 is constituted by a frequency dividing circuit, it can be constituted by a digital circuit, which facilitates power saving and LSI implementation.

Furthermore, in order to return the external clock pulse to the internal clock pulse, since the off-state of the external voltage is detected, the I
Since there is no need to issue commands from the C card reader/writer and clock switching is limited to one-way switching from the external clock to the internal clock, it is possible to prevent erroneous operation due to static electricity, etc. during stand-alone operation.

(b) Description of other embodiments In addition to the embodiments described above, the present invention can be modified as follows.

(2) Although the external clock detection circuit 8 is constituted by a frequency dividing circuit, it may be constituted by an integrating circuit.

(2) To return the external clock pulse to the internal clock pulse, the off-state of the external voltage is detected, but an end command may also be used. Alternatively, a watchdog timer may be used that forces the processor to reset if the flag is not reset within a certain period of time.

The present invention has been explained above using examples, but
Various modifications are possible within the scope of the present invention, and these are not excluded from the scope of the present invention.

[0044]

[Effects of the Invention] As explained above, according to the present invention,
It has the following effects.

(2) Since the processor 1 detects that the external clock pulse is reliably received and switches the internal clock pulse to the external clock pulse, no malfunction will occur even if something touches the external terminal during stand-alone operation.

(2) Malfunctions do not occur even if no external clock pulse is output.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention.

FIG. 2 is an explanatory diagram of an IC card according to an embodiment of the present invention.

FIG. 3 is a block diagram of an IC card according to an embodiment of the present invention.

FIG. 4 is a flowchart of clock switching processing according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of the operation of one embodiment of the present invention.

FIG. 6 is an explanatory diagram of the prior art.

[Explanation of symbols]

1 Processor 2 Internal clock source 3. Memory 4 Input section 5 Display section 6 Battery 7 External connection terminal 8 External clock detection circuit 9 External voltage detection circuit

Claims (4)

[Claims] 1. An internal clock source (2) that generates internal clock pulses, a processor (1) that operates according to an operating clock, and an input section (4) for inputting data.
, a display section (5) that displays data, and a battery for operation (
6) and an external connection terminal (7), an external clock detection circuit (8) for detecting an external clock pulse from the external connection terminal (7) is provided,
A clock for an IC card, characterized in that the processor (1) checks an external clock pulse based on the output of the external clock detection circuit (8) and switches the operating clock from the internal clock pulse to the external clock pulse. How to switch. 2. The external clock detection circuit (8) comprises:
The external clock pulse is frequency-divided and the processor (1
2. The IC card clock switching method according to claim 1, wherein said external clock pulse is confirmed from said frequency-divided output in accordance with said internal clock pulse. 3. The processor (1) switches the operating clock from the external clock pulse to the internal clock pulse in response to a termination command from the external connection terminal (7). How to change the clock of an IC card. 4. An external voltage detection circuit (9) is provided for detecting an external voltage from the external connection terminal (7), and the processor (1) detects that the external voltage is no longer applied; 2. The IC card clock switching method according to claim 1, wherein the operating clock is switched from the external clock pulse to the internal clock pulse.