JPH06150029A - Reset controller - Google Patents

Abstract

PURPOSE:To provide the reset controller which can change the reset cycle of a microcomputer corresponding to the power supply voltage lowering state of the microcomputer. CONSTITUTION:This controller is provided with an order circuit 12 for comparing a stablized power supply voltage level with reference levels Hth and Lth by voltage monitor circuits 10 and 11 and for deciding a first state in which the power supply voltage level is higher than the relatively higher level Hth, a second state in which the power supply voltage level is lower than the level Hth, and a third state in which the power supply voltage level is lower than the relatively lower level Lth, when the decided result is transited between the first state and the second state, a microcomputer 1 is reset in a cycle corresponding to the cycle of the second state and when the judged result is transited while including the third state as well, the microcomputer 1 is reset while exceeding a cycle corresponding to the cycles of second and third states.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reset control device applied to a microcomputer system, and more particularly to a technique effective for use in a microcomputer system in which safety is important, such as an automobile engine control system. is there.

[0002]

2. Description of the Related Art Conventionally, a power supply control IC has been provided for a microcomputer system. Such a power supply control IC includes a circuit that supplies a stabilized power supply to a microcomputer and a circuit that monitors an abnormal loop or runaway of a program of the microcomputer. When a runaway is detected, the microcomputer is reset and when the power is turned on. It outputs a signal for holding the reset state (power-on reset) for a certain period necessary for stabilizing the operating state of the internal circuit such as the oscillation circuit. An example of a document describing such a power supply control IC is "HD6301" issued by Hitachi, Ltd. in March 1987.
Y0, HD6303Y Application Note: Hardware Edition ”, pages 232 to 233.

Further, in addition to the above, the present inventor has found that it is necessary to monitor the power supply voltage of the microcomputer and put the microcomputer in the reset state even when the voltage falls below a specified voltage. When the power supply voltage of the microcomputer becomes equal to or lower than the specified voltage, for example, after the contents of the register of the microcomputer are stored in another storage device (such as SRAM), the microcomputer is initialized by a procedure. Prevent malfunction of computer system. For that purpose, in addition to the conventional power supply control IC described above, an IC for monitoring the power supply voltage or a circuit composed of a discrete device such as a transistor can be added.

At this time, since the power-on reset is performed when the power is turned on, the microcomputer is kept in the power-on reset state for a certain period as in the case where the power is turned on even when the power supply voltage momentarily becomes lower than the specified voltage. can do.

[0005]

However, when the power supply voltage of the microcomputer becomes lower than the specified voltage, the power-on reset similar to that at the time of power-on is performed in any case. During the relatively long period in which the reset is performed, the microcomputer cannot control the target system substantially.
For example, in a vehicle-mounted microcomputer system such as an automobile engine control system or a brake control system, substantial control over the engine and the brake cannot be performed while the microcomputer is in a reset state. Such a control suspension period is absolutely short, but in order to ensure the safety and operability of the system, the shorter the substantial uncontrollable period, the better. In this respect, the present inventor determines the state of the decrease in the power supply voltage of the microcomputer and maintains the reset state for a relatively long period such as power-on reset only when necessary to improve system safety and safety. We have found the necessity of ensuring operability.

It is an object of the present invention to provide a reset control device capable of changing the reset period of a microcomputer according to the power supply voltage drop state of the microcomputer.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0008]

The outline of the representative one of the inventions disclosed in the present application will be briefly described as follows.

That is, the voltage level of the power supply used in the microcomputer is compared with a plurality of reference levels having different levels by the comparison means, and the voltage level of the power supply to be compared is determined based on the comparison result. A first state having a higher level than the reference level having a relatively higher level in the absolute sense, a second state having a lower level than the reference level, and a reference having a lower level in the absolute sense When the determination means capable of determining the third state whose level is lower than the level is provided and the determination result by the determination means transits between the first state and the second state, the period corresponding to the period of the second state is set. Accordingly, the reset signal of the microcomputer is maintained at the reset instruction level, and when the determination result by the determination means changes including the third state, the second and third states Beyond period to comply in time to adopt the reset signal generating means for maintaining said reset signal to the reset instruction level.

When the stabilized power supply circuit is built in, the comparison means can compare the voltage level of the external power supply or the stabilized power supply to be output.

In order to add a function of monitoring an abnormal loop or runaway of the microcomputer, the counting operation is reset at every predetermined cycle of the program running pulse signal of the microcomputer, and the reset signal is generated by the overflow of the counting operation. Provide a watchdog timer.

[0012]

According to the above means, the reset signal generating means is responsive to the power supply voltage drop state of the microcomputer determined by the determining means based on the comparison result of the comparing means.
The reset period of the microcomputer can be changed. This means that even if the power supply voltage of the microcomputer momentarily drops below the specified voltage, it is possible to restart the microcomputer promptly without maintaining the power-on reset state as in the case of turning on the power. Therefore, only when necessary, the reset state is maintained for a relatively long period such as power-on reset to ensure the safety and operability of the system.

[0013]

FIG. 1 shows an embodiment of a reset control device according to the present invention.

In FIG. 1, reference numeral 1 is a microcomputer integrated into a semiconductor circuit for overall control of a microcomputer system, 2 is a reset control device of this embodiment, and other peripheral circuits are omitted. is there.
Although not particularly limited, the reset control device 2 of the present embodiment is formed on one semiconductor substrate such as single crystal silicon by a known semiconductor integrated circuit manufacturing technique. Although not particularly limited, the microcomputer system partially shown is a system such as an engine control system or a brake control system of an automobile, which requires safety and operability of controlled equipment. Reset control device 2
Is a power supply terminal 5 to which an external power supply 4 such as a 12 V battery is supplied via the external power supply switch 3, a power supply terminal 6 for outputting a stabilized power supply such as 5 V, and a reset signal RE.
The S output terminal 7 and the input terminal 8 for the periodic signal such as the program running pulse signal PRP are provided. The stabilized power supply is formed by a stabilized power supply circuit 9 which inputs an external power supply. The stabilized power supply circuit 9 may be composed of a known series regulator or switching regulator, although not particularly limited. The reset signal RE
S is supplied to the reset terminal 70 of the microcomputer 1. The program running pulse signal PRP is output from a predetermined port 80 of the microcomputer 1. The power supply control circuit 2 includes two voltage monitoring circuits 10 and 11, a sequential circuit 12, and a reset signal output control circuit 13 for power supply monitoring, and also for monitoring a runaway or abnormal loop of the microcomputer 21. Has a watchdog timer 14.

The voltage monitoring circuits 10 and 11 constitute a comparison means for comparing the voltage level of the stabilized power supply to be output from the power supply terminal 6 with a plurality of reference levels (also referred to as voltage monitoring levels) having mutually different levels. However, for example, one voltage monitoring circuit 10 sets the voltage level of 2/3 of the voltage level of the stabilized power supply as the reference level (Hth), and the other voltage monitoring circuit 11 sets the voltage level of 1/3 of the voltage level of the stabilized power supply. The voltage level is set to the reference level (Lth), and the comparison result is set to logic "1" when the input is below the reference level.

The sequential circuit 12 includes the voltage monitoring circuit 1
When the comparison result of 0 and 11 is input, the voltage level of the stabilized power supply is higher than the reference level level Hth in the absolute value sense.
The second state whose level is lower than th and the third state whose level is lower than the reference level Lth in the absolute value sense are determined. According to this embodiment, both voltage monitoring circuits 1
When the outputs of 0 and 11 are logic "1", the first state, when the output of only one voltage monitoring circuit 10 is logic "1", the second state, the outputs of both voltage monitoring circuits 10 and 11 are logic When it is "1", it is determined to be the third state.

The reset signal output control circuit 13 has a period corresponding to the period of the second state when the determination result by the sequential circuit 12 transits between the first state and the second state. When the reset signal RES is maintained at the reset instruction level and the determination result by the sequential circuit 12 changes including the third state, the reset signal RES is exceeded beyond the period corresponding to the periods of the second and third states.
To the reset instruction level. That is, as shown in FIG. 2, when the voltage level of the stabilized power supply returns to the specified voltage level after passing through the second state, the reset signal RES is reset to the reset enable level (main) during the period of the second state. According to the embodiment, the low level). In FIG. 2, the state of the microcomputer corresponding to the period of the second state is simply described as reset. When the voltage level of the stabilized power supply changes including the third state, even if the voltage level of the stabilized power supply returns to the specified voltage level, not only the period of the second state but also the fixed period of time after which the state returns to the first state. Further, the reset signal is maintained at the reset enable level. In FIG. 2, the state of the microcomputer corresponding to a certain period after returning from the second state to the first state is simply described as power-on reset.

The watchdog timer 14 has a program running pulse signal P supplied to the input terminal.
The counting operation is reset every predetermined cycle of RP, and the overflow of the counting operation generates the reset signal RES to be output from the reset terminal 7. The program running pulse signal PRP is a signal that is changed with a cycle every time the microcomputer executes a predetermined routine of its operating program, and has a certain allowable range when the microcomputer is operating normally. Therefore, the cycle is only changed, and once an abnormal loop or runaway occurs in the microcomputer, the cycle is changed beyond the allowable range. The watchdog timer 14 detects that an abnormal loop or runaway has occurred in the processing of the microcomputer 1 from such a change in the cycle and resets the microcomputer. The reset signal output by the watchdog timer 14 and the reset signal output by the reset signal output control circuit 13 are given to the external terminal 7 via the OR gate 15, for example.

FIG. 2 is a timing chart showing an example of the reset operation associated with the power supply voltage drop in the microcomputer system shown in FIG.

When power is applied to the reset control device 2 from the external power supply 4, the stabilizing power supply circuit 9 causes the stabilizing power supply to be supplied to the microcomputer 1. At this time, in the process in which the power to be supplied to the microcomputer 1 rises to the stabilized voltage, the power supply voltage of the microcomputer 1 transits between the third state and the second state, and the power supply voltage is set in the voltage monitoring circuit 10. Reset signal RES until the voltage monitoring level Hth becomes equal to or higher than
Is at a low level and the microcomputer 1 is in a reset state. At this time, since the sequential circuit 12 recognizes that it was in the third state before the second state, the reset signal is further set to the low level for a certain period from the time when the power supply voltage becomes equal to or higher than the voltage monitoring level Hth. Then, the microcomputer 1 is kept in the power-on reset state. After the lapse of the power-on reset period, the reset signal RES is set to the high level and the reset state of the microcomputer is released. After that, the microcomputer 1 starts the operation according to the operation program.

When the power supply voltage to the microcomputer is lowered by the influence of external noise during the operation of the microcomputer and becomes lower than the voltage monitoring level Hth, the reset signal RES is set to the low level (reset state). If the power supply voltage at this time is instantaneously decreased and the power supply voltage rises without falling below the voltage monitoring level Lth set in the voltage monitoring circuit 11, the reset signal is output at the time when the power monitoring voltage rises above the voltage monitoring level Hth. RES is set to high level (reset state is released).

When the power supply voltage drops significantly and drops below the voltage monitoring level Lth, the power supply voltage remains above the voltage determination level Hth even after the power supply is restored to the first state. After that, the reset signal RES is set to the low level for a certain period, and the microcomputer 1 is brought into the power-on reset state.

According to this embodiment, there are the following effects. (1) When the power supply voltage of the microcomputer 1 drops to the voltage monitoring level Lth, the microcomputer 1
To prevent the malfunction of the system by controlling the reset state and the power-on reset state, but when the power supply voltage rises without lowering to the voltage monitoring level Lth or less, the microcomputer 1 is in the power-on reset state. Promptly release the reset state without shifting to
Minimize the control pause period of the microcomputer. As a result, even if the power supply voltage of the microcomputer 1 momentarily falls below the specified voltage, the microcomputer 1 can be restarted promptly without having to reset the microcomputer 1 for a certain period of time as when the power is turned on. become. (2) From the above, in a vehicle-mounted microcomputer system such as an automobile engine control system or a brake control system, the situation in which the control suspension period becomes unnecessarily long is prevented, and the safety and operability of the system are ensured. be able to. (3) The reset control device of the above embodiment is made into one semiconductor integrated circuit. If a similar configuration is realized by using a general-purpose logic IC such as a flip-flop, it goes against the demands for downsizing the microcomputer system and simplifying the circuit configuration or reducing the number of circuit parts. When an IC is used to configure a power supply voltage drop state determination circuit, the number of components becomes large and the connections between components become complicated, and it is difficult to adjust interface timing due to variations in the characteristics of each component. Become. Therefore, the single semiconductor integrated reset control device of this embodiment can perform the reset control of the microcomputer with high reliability.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited thereto, and needless to say, various modifications can be made without departing from the scope of the invention. Yes.

For example, the present invention can be applied to a configuration in which three or more types of voltage monitoring levels are provided and the voltage before stabilization is monitored. In addition, the first to third states of the power supply voltage drop are determined by directly determining the voltage level, and pseudo determining the first to third states based on the length of time that the voltage is below one voltage determination level. It is also possible to do so. Further, when the fluctuation factor of the power supply voltage is exclusively due to the external power supply such as a battery, the power supply voltage to be compared may be the external power supply voltage. The reset control device of the present invention is not limited to the one configured as a dedicated single LSI as in the above embodiment,
It may be built in the microcomputer. In this case, the stabilized power supply circuit is externally attached.

In the above description, the case where the invention made by the present inventor is mainly applied to the vehicle-mounted microcomputer system which is the background field of application has been described, but it can be applied to other various microcomputer systems. . The present invention can be applied at least under the condition that the reset period of the microcomputer is changed according to the power supply voltage drop state of the microcomputer.

[0027]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) The reset signal generating means can change the reset period of the microcomputer according to the state of the power supply voltage drop of the microcomputer judged by the judging means based on the comparison result of the comparing means. Even when the power supply voltage of the computer instantaneously becomes equal to or lower than the specified voltage, it is possible to promptly restart the microcomputer without maintaining the microcomputer in the power-on reset state as when the power is turned on. (2) As a result, the reset state is maintained for a comparatively long period such as a power-on reset only when necessary, and the control pause period in the microcomputer system is not unnecessarily lengthened, thereby ensuring system safety and operation. You can take full care of your sex. (3) Since the semiconductor integrated circuit is used, the reset control of the microcomputer can be performed with high reliability. (4) By further incorporating a watchdog timer, a function of monitoring an abnormal loop or runaway of the microcomputer can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a reset control device according to the present invention.

FIG. 2 is a timing chart showing an example of a reset operation associated with a decrease in power supply voltage in the microcomputer system shown in FIG.

[Explanation of symbols]

 1 Microcomputer System 2 Reset Control Device 5 Power Supply Terminal 6 Power Supply Terminal 9 Stabilized Power Supply Circuit 10, 11 Voltage Monitoring Circuit Hth, Lth Voltage Monitoring Level 12 Sequence Circuit 13 Reset Signal Output Control Circuit 14 Watchdog Timer RES Reset Signal PRP Program Running Pulse signal

Claims (3)

[Claims] 1. A comparison means for comparing a voltage level of a power supply used in a microcomputer with a plurality of reference levels having mutually different levels, and a voltage of the power supply to be compared based on a comparison result of the comparison means. The level is a first state having a higher level than the reference level having a relatively higher level in the absolute sense, a second state having a lower level than the reference level, and a relatively level in the absolute sense. Determination means capable of determining the third state having a level lower than the low reference level, and when the determination result by the determination means transits between the first state and the second state, the period corresponding to the period of the second state. Accordingly, the reset signal of the microcomputer is maintained at the reset instruction level, and when the determination result by the determination unit changes including the third state, the second and third states Reset control and wherein the the reset signal generating means for maintaining the reset instruction level the reset signal over a period of meeting between are those comprising on a single semiconductor substrate. 2. A stabilizing power supply circuit which receives an external power supply and stabilizes and outputs the external power supply, wherein the comparison means has a plurality of voltage levels of the external power supply or the stabilized power supply to be output, which are different in level from each other. The reset control device according to claim 1, wherein the reset control device compares the reset control device with the reference level. 3. A watchdog timer for resetting the counting operation every predetermined period of the program running pulse signal of the microcomputer system, and for generating a reset signal for the microcomputer based on the overflow of the counting operation. 3. The reset control device for a microcomputer system according to claim 1, wherein the reset control device is provided.