JPH10269327A - Control circuit - Google Patents

Abstract

(57) [Summary] A reset circuit for a microcomputer such as an IC card, in which the reset is released when there is not enough power supply voltage for the operation of the microcomputer, or the reset is started when the power is not supplied. The inconvenience of supplying each signal is solved. A power supply of an output circuit such as a reset signal supplied to a microcomputer in an interface unit is made common to a power supply supplied to the microcomputer. As long as the operation of the logic circuit cannot be guaranteed, this power supply is turned off by a reset operation based on analog detection not depending on the logic circuit. Further, analog detection is performed by detecting an output voltage of a power supply generation circuit provided separately from a power supply generation circuit provided to the microcomputer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reset circuit for initializing the operation of, for example, a microcomputer (hereinafter abbreviated as "microcomputer"), and to a reset circuit.

[0002]

2. Description of the Related Art An IC card which has a microcomputer, a memory, and a control circuit in the card and transmits / receives information to / from a reader / writer (hereinafter abbreviated as R / W) has reached the stage of practical use, and has been rapidly developed. It is proceeding with. Based on the signal received from the R / W, the card performs not only demodulation and data processing, but also power generation and signal processing clock regeneration.
Also, it generates information to be sent to the R / W (data reading and modulation). These card-side functions will be performed in a single-chip LSI in the future, but currently, the microcomputer and the interface unit (power supply, clock generation, modulation and demodulation,
In many cases, another chip is used for microcomputer control).

Recently, transmission / reception between the R / W and the card has been
A non-contact type is under study, such as a method using electromagnetic coupling using a coil.

[0004] These matters are described, for example, by Katsuru Sunagawa and Hiroyuki Kikui, "IC Card Development and Mechanism in Latest Patents".
p. 51-59 (published by the Industrial Research Association, 1988).

[0005]

A problem that always arises in a circuit having a built-in microcomputer is a reset method for initializing the operation when the power supply rises or momentary interruption occurs.

[0006] The microcomputer and the interface unit are connected to logic signals such as data, clock, reset, and the like by a power supply. Considering the time when the power supply rises, it is not desirable from the viewpoint of the structure of the semiconductor that another signal is supplied at a logic high before the power supply is supplied to the microcomputer. The reset signal therefore normally resets a logic low. data,
The clock and the like must control the timing given to the microcomputer. Also, the reset signal itself cannot guarantee a logic low unless the power supply voltage is high enough to allow the logic circuit to operate normally, and in this case, the reset is released before a sufficient voltage is supplied to the microcomputer. Occurs.

[0007] Since the IC card does not operate with a large-capacity power supply but uses a small-capacity and somewhat unstable power supply, the reset operation particularly requires reliability.

[0008] This problem is not disclosed in the literature.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for solving the above problems.

First, the power supply of an output circuit such as a reset signal applied to the microcomputer in the interface unit is made common to the power supply applied to the microcomputer. Second, while the operation of the logic circuit cannot be guaranteed, this power is turned off by a reset operation based on analog detection that does not depend on the logic circuit.
Do not give to the above output circuit and microcomputer.

Further, if necessary, the analog detection is performed by detecting the output voltage of a power supply generating circuit provided separately from the power supply generating circuit provided to the microcomputer. Further, the circuit configurations of the generator circuits of both power supplies are the same.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a circuit of an IC card showing a first embodiment of the present invention. 1 is a coil, 2 is a rectifier bridge circuit, 3 is a smoothing capacitor, 4 is a clock recovery circuit, 5 is a demodulation circuit, 6 is a modulation circuit, 7 is a reset generation circuit, 8 is a comparison circuit, 9 is a regulator circuit, 10 is A regulator circuit, 11 is a reference voltage generating circuit, 12 is a comparing circuit, 121 is a resistor, 122 is a diode, 13 is a switch, 14 is an AND circuit, 15a to 15d are buffer circuits, 16 is a microcomputer, and 17 is a memory.

The overall operation will be described. First, R from the card
/ W when the signal is transmitted from the memory 17 under the control of the microcomputer 16 to the buffer circuit 15c.
To the modulation circuit 6 via Here, modulation is performed so that signals can be exchanged with the R / W. Recently, standards for performing two-phase PSK modulation have been proposed. The modulated signal changes the load current of the rectifier bridge circuit, and is transmitted from the coil 1 to a coil (not shown) on the R / W side by electromagnetic coupling.

The received signal input to the coil 1 from the R / W side is supplied to a clock recovery circuit 4 and a demodulation circuit 5.
After the reproduction of the reference clock and the demodulation of the received data,
The data is sent to the microcomputer 16 via the buffer circuits 15a and 15b and stored in the memory 17 as needed. Similarly, the signal input to the coil 1 is rectified by the action of the rectifying bridge circuit 2 and the smoothing capacitor 3. This is a power source for the regulator circuit 9, the second regulator circuit 10, and the reference voltage generation circuit 11. The regulator circuit 9 obtains a constant voltage having little dependence on the level of the received signal, and supplies power to the microcomputer 16. The regulator circuit 10 similarly obtains a constant voltage and supplies power to the clock recovery circuit 4, demodulation circuit 5, and modulation circuit 6 and the like, and is also applied to one end of a comparison circuit 8 as described later. The output voltages of the regulator circuits 9 and 10 may be the same or different. The reference voltage generation circuit 11 is a generation circuit of a constant potential using a band gap voltage or the like, and has very little dependence on a power supply voltage, temperature, and the like. Therefore, it is used as a reference potential when the regulator circuits 9 and 10 generate a constant voltage. It is also provided to the other end of the comparison circuit 8.

Although not shown, the power of the comparison circuit 8 is supplied from the output of the regulator circuit 10, and the power of the comparison circuit 12 is supplied from the smoothing capacitor 3.

The comparison circuit 8 determines which of the output voltages of the regulator circuit 10 and the reference voltage generation circuit 11 is higher. During normal operation, the former has a higher potential. However, since the rise of the operation of the regulator circuit or the like is slow, the latter has a higher potential at the moment when the card and the R / W are first combined. At this time, the microcomputer is reset because the power supply voltage applied to the microcomputer is insufficient to obtain a stable operation. For this reason, the reset generation circuit 7 generates a reset signal based on the comparison result of the comparison circuit 8. This signal is sent to the microcomputer 16 via the buffer circuit 15d.
Given to. For this reason, the reset is released and the microcomputer 16 operates only when there is a power supply voltage sufficient for stable operation.

As long as the operation of the logic circuit including the reset generation circuit 7 is not stable, the output of the buffer circuit 15d is not always the expected signal. When the power supply voltage is low, the output of the regulator circuit 9
Before being given to 6, a reset release signal may be issued. In this case, the voltage of the other terminals becomes higher than that of the power supply terminal of the microcomputer 16, which may cause destruction or malfunction of the device. The same can occur at the clock and data terminals. A first feature of the present invention is to disclose a solution to this problem.

In FIG. 1, for this purpose, first, a switch 13 is provided in a path of a reference voltage to be supplied to the regulator circuit 9, and the switch 13 is cut off unless there is a sufficient voltage for operation so that power is not supplied to the microcomputer. I do. And the buffer circuit 15
By connecting the same power supply as the microcomputer to a to 15d,
The voltage of the other terminals of the microcomputer does not exceed the voltage of the power supply terminal.

The switch 13 performs a switching operation using the logic generated by the AND circuit 14 so that a malfunction does not occur during a period in which the operation of the logic circuit including the reset generation circuit 7 is unstable. The AND circuit 14 calculates the logical product of the outputs of the reset generation circuit 7, the comparison circuit 8, and the comparison circuit 12. Since this AND circuit 14 can be realized by simple transistor logic, it can operate stably even when the power supply voltage is low. The comparison circuit 12 compares the output of the reference voltage generation circuit 11 with the forward voltage of the diode 122. In general, attention is paid to the fact that the forward voltage of the diode 122 obtained by the bias current from the resistor 121 rises quickly. Until the reference voltage generating circuit 11 rises, the switch 13 is surely turned in the opposite direction to that shown in the figure. To prevent the regulator circuit 9 from accidentally starting up. The comparison circuit 8 compares the outputs of the regulator circuit 10 and the reference voltage generation circuit 11. In general, attention is paid to the fact that the latter rises earlier than the former, and the switch 13 is connected in the opposite direction to that shown until the regulator circuit rises. As described above, a method based on analog detection, which does not depend on a logic circuit, is also used.

Therefore, the output of the AND circuit 14 becomes logic high and the switch 13 is connected as shown when the reset release signal is generated by the reset generation circuit 7 without causing a logic malfunction.

As described above, in the embodiment of FIG. 1, the power supply of the microcomputer and the common line is supplied to the buffer circuits 15a to 15d, and this power supply is surely turned off unless the operation of the logic circuit can be guaranteed. For this reason, it is possible to eliminate the inconvenience that the reset is erroneously released while the voltage is low and that the voltage of the power supply terminal or more is supplied to each terminal of the microcomputer.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a circuit block diagram showing an embodiment of the present invention. 2 differs from the embodiment of FIG. 1 in that one end of the input terminal of the comparison circuit 12 is connected to the output of the regulator circuit 10 instead of the output of the reference voltage generation circuit 11.

Although the regulator circuits 9 and 10 depend on the circuit type, if a sufficient margin is provided for the oscillation phenomenon,
The rising at the time of power-on becomes somewhat gentle, and the delay becomes larger than the rising of the reference voltage generating circuit 11. In this case, in the embodiment of FIG. 1, before the comparison circuit 8 reaches the power supply voltage for normal operation, the output of the comparison circuit 12
Further, the output of the AND circuit 14 becomes high, and power may be supplied to the microcomputer 16 before there is a power supply voltage sufficient for operation.

The embodiment shown in FIG. 2 provides a solution to such an inconvenience.
Is applied to the comparison circuit 12, the above-described inconvenience can be avoided even when the rise of the regulator circuit is slow.

Although there are many types of regulator circuits, it is desirable that the regulator circuit 9 and the regulator circuit 10 have exactly the same circuit configuration. In that case, even if the output voltage values are different, the rise times of both are almost the same. Therefore, the problem that the rise time is different between the two regulators and the voltage of the regulator circuit 10 reaches a sufficient value while the output voltage of the regulator circuit 9 is insufficient and the reset is released can be solved.

[0027]

According to the present invention, in a reset circuit of a microcomputer such as an IC card, the reset is released when there is not enough power supply voltage for the operation of the microcomputer, or the reset is started when the power is not supplied. The inconvenience of supplying each signal as described above can be solved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Coil, 2 ... Rectifier bridge circuit, 3 ... Smoothing capacitor, 4 ... Clock regeneration circuit, 5 ... Demodulation circuit, 6 ... Modulation circuit, 7 ... Reset generation circuit, 8 ... Comparison circuit, 9 ... Regulator circuit, 10 ... Regulator circuit, 11: Reference voltage generation circuit, 12: Comparison circuit, 121: Resistor, 122: Diode, 13: Switch, 14: AND circuit, 15: Buffer circuit, 16: Microcomputer, 17: Memory.

Claims (3)

[Claims] 1. A medium containing a microcomputer,
In a system including a reader / writer for exchanging data with the medium, a circuit for generating a reset signal for initializing the operation of the microcomputer, a buffer circuit for supplying the reset signal to the microcomputer, and a power supply for supplying power to the microcomputer. A generator circuit at least in the medium,
A control circuit, wherein a power supply to the microcomputer is supplied to a power supply of the buffer circuit. A second voltage generating circuit provided in the medium, separately from a power generating circuit for supplying power to the microcomputer; an output of the reset signal generating circuit and an output of the second voltage generating circuit; By logical product with the logical signal corresponding to the level,
2. The control circuit according to claim 1, wherein the control circuit switches the supply of power to the microcomputer. 3. The control circuit according to claim 2, wherein the circuit configuration of said power supply circuit for supplying power to said microcomputer and said second voltage generation circuit are the same.