JPS63268043A - Resetting system for microcomputer - Google Patents

Abstract

PURPOSE:To eliminate an exclusive port and to simplify the constitution of a microcomputer resetting system by using a watchdog timer which is reset by a pulse train of the input/output data. CONSTITUTION:The input/output data are periodically transferred via a bus 8 as long as a microcomputer 9 is normally operating. thus a watchdog timer 12 is reset by a trigger circuit 11 and a resetting signal is never given to the microcomputer 9. While the periodical transfer of the input/output data is not carried out any more when the microcomputer has a runaway. Then a data input/output port of the microcomputer 9 is fixed at an H or L level and there fore the timer 12 is not reset by the circuit 11. As a result, a resetting signal is applied to the microcomputer 9 from the timer 12 passed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a microcomputer reset method,
For example, it can be effectively used as a reset method for a microcomputer in an IC card read/write device.

[Description of Prior Art] As a reset method when a microcomputer runs out of control,
A device using a watchdog timer is known. In the conventional reset method of this type, one port of the microcomputer is assigned to the watchdog timer.
A pulse train indicating the normal operation of the program is given to the watchdog timer from the microcomputer.
The microcomputer is reset by a reset signal generated by the watchdog timer when the pulse train is no longer applied during runaway.

According to such a conventional reset method, it is necessary to allocate one boat for the watchdog timer, which not only makes it impossible to provide a reset means when there is not enough board space, but also prevents the pulse train from being generated during normal operation. It is troublesome that it is necessary to incorporate the command to give the program into the program.

[Object of the Invention] The present invention has been made based on the above-mentioned viewpoints, and its object is to eliminate the need to allocate a dedicated port and to incorporate into a program an instruction for providing a pulse train for the watchdog timer. The object of the present invention is to provide a microcomputer reset method using a watchdog timer.

[Means for achieving the object] In the present invention, in a microcomputer that periodically transmits and receives input/output data through serial communication, a watchdog timer that is reset by a pulse train of the input/output data is provided, and the watchdog The above object is achieved by a microcomputer reset method that provides a reset signal from the watchdog timer to the microcomputer when the timer is not reset.

In other words, in a microcomputer that regularly sends and receives input/output data via serial communication, the runaway causes data to no longer be sent and received regularly, and the watchdog timer is not reset, causing the watchdog timer to reset the microcomputer. A signal will be given.

[Embodiment of the Invention] FIG. 1 is a block diagram showing an embodiment of the present invention, in which it is applied to an IC card reading/writing device, where l is an IC card, and 2 is an IC card 1 reading/writing device. It is a device.

The IC card 1 has a built-in electrically rewritable non-volatile memory 3 (EEPROM) and a CPU 4 that controls reading and writing of the memory 3, and has a reading/writing device 2 and a reading/writing device 2 for reading and writing the memory 3 and CPU 4 on its surface. 6 for connecting
exposed contacts 5a to 5f. Contact 5a is a clock input contact, contact 5b is a reset input contact, contact 5C
is a data input/output contact, contact 5d is an operating power input contact, contact 5e is a write power input contact, and contact 5f is a ground contact.

The read/write device 2 includes six contact pins 6a to 6f that make electrical contact with the contacts 5a to 5f of the IC card 1. The contact pin 6a is for a clock, is connected to an off-silver turret that provides a clock signal, and comes into contact with a contact 5a of the IC card 1. The contact pin 6b is for resetting and is connected to the microcomputer 9.
It makes contact with the contact 5b of the IC card l. contact pin 6
C is for data input/output, and is connected to the data input/output port of the microcomputer 9 via the data input/output line 8, and comes into contact with the contact 5C of the IC card l. The contact pin 6d is for supplying operating power, is connected to the power supply circuit 10, and comes into contact with the contact 5d of the IC card l. The contact pin 6e is for supplying write power, is connected to the power supply circuit 10, and comes into contact with the contact 5e of the IC card l.

The contact pin 6f is for ground and makes contact with the contact 5f of the IC card 1.

11 is a trigger circuit whose input terminal is connected to the data input/output line 8 and whose output terminal is connected to the reset input terminal of the watchdog timer 12. The trigger circuit 11 receives a pulse train of input/output data from the data input/output line 8,
The watchdog timer 12 is reset every time a pulse is input. The watchdog timer 12 has its reset signal output terminal connected to the reset signal input port of the microcomputer 9, and outputs a reset signal to the microcomputer 9 over time based on the time constant circuit 13 when not reset by the trigger circuit 11. do.

14 is a transfer roller for carrying in and carrying out the IC card l;
5 is a motor that drives the transfer roller 14, 16 and 17
is a limit switch for detecting the insertion of the IC card 1 and the completion of loading.

The motor 15 is under the control of the microcomputer 9 via a motor drive circuit 18. The limit switches 16 and 17 are connected to the microcomputer 9, and the microcomputer 9 inserts the IC card 1, recognizes the completion of loading, and controls the motor, so that the contacts 5a to 5f and the contact pins 6& to 6f are in contact with each other. The IC card 1 is to be transported.

With the above configuration, the contacts 5a to 5f are brought into contact with the contact bins 6a to 6f, and reading and writing to the IC card 1 is performed by transmitting and receiving input/output data through serial communication between the CPU 4 and the microcomputer 9. The input/output data is as shown by reference symbols A and B in FIG.
It is composed of multiple bits including a start bit, information bit, and parity bit, and is periodically transmitted and received at a predetermined time width T. The time constant of the time constant circuit 13 is selected such that if the watchdog timer 12 is not reset by the trigger circuit 11 for a time longer than the time width T, a reset signal is given from the watchdog timer 12 to the microcomputer 9. There is. If the microcomputer 9 is operating normally, input/output data is sent and received regularly, so the watchdog timer 12 is reset by the trigger circuit 11, and no reset signal is given to the microcomputer 9.
On the other hand, if the microcomputer 9 goes out of control,
Regular transmission and reception of input/output data is no longer performed, and the data input/output port of the microcomputer 9 is kept at a constant H or L level, so that the trigger circuit 11 no longer resets the watchdog timer 12.

As a result, a reset signal is given from the watchdog timer 12 to the microcomputer 9 after a period of time based on the time constant circuit 13.

Although the above embodiment describes the application to an IC card reading/writing device, the application is not limited to this, but can be widely applied as a reset method for a microcomputer that periodically sends and receives input/output data through serial communication. be able to.

[Effects of the Invention] As explained above, the present invention focuses on the fact that in a microcomputer that regularly transmits and receives input and output data through serial communication, the regular transmission and reception of data becomes impossible due to runaway. If the watchdog timer is not reset by the input/output data pulse train, the watchdog timer outputs a reset signal to reset the microcomputer, so there is no need to allocate a dedicated port, and the watchdog It is possible to provide a microcomputer reset method that does not require incorporating into a program an instruction for providing a pulse train for a timer.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram of input/output data. 8...Data input/output line 9...Microcomputer 11...Trigger circuit 12...Watchdog timer

Claims (1)

[Claims] A microcomputer that periodically sends and receives input/output data via serial communication has a watchdog timer that is reset by a pulse train of the input/output data, and when the watchdog timer is not reset, the microcomputer A microcomputer reset method characterized in that a reset signal is given to the computer.