JPH0227684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a memory backup device for a vehicle-mounted microcomputer, and more particularly to a device for confirming memory backup.

<Background Art> For example, an on-vehicle microcomputer that centrally controls an internal combustion engine mounted on a vehicle requires data from the previous operation when starting its operation. This type of in-vehicle microcomputer continues to supply power to the RAM (Random Access Memory) from the battery via the backup power supply circuit even after the power supply to the CPU (Central Processing Unit) is stopped due to the ignition switch being turned off. It has a memory backup device that retains data in RAM until the next operation.

However, with this type of memory backup device, if the microcomputer unit is removed from the vehicle or the power line is disconnected,
If the power supply to RAM is interrupted, data stored in RAM will not be retained correctly. Then, the next operation of the microcomputer is performed based on this incorrectly stored data, so that proper operation control is not performed.

In this way, conventional in-vehicle microcomputers cause the above-mentioned inconveniences because they read the memory contents of RAM at the start of operation without confirming whether or not they have been destroyed due to the power supply to the RAM being stopped. It was hot.

<Purpose> Therefore, in order to avoid such inconveniences, the present invention provides a backup confirmation device that confirms whether data stored in RAM has been destroyed due to the power supply to the RAM being stopped when the in-vehicle microcomputer starts operating. The purpose is to provide.

<Summary of the Invention> To this end, a flip-flop circuit outputs a signal when a signal is input to a set terminal, and stops outputting the signal when a signal is input to a reset terminal;
The battery is removed through the backup power supply circuit.
power supply restart signal output means for outputting a signal to the set terminal of the flip-flop circuit when connected to the RAM; A backup confirmation device is constituted, comprising a reset signal output means for outputting a reset signal to a reset terminal, and a detection means for detecting whether an output signal from the flip-flop circuit is being transmitted when the on-vehicle microcomputer is powered on. .

According to this, the power supply restart signal output means outputs a signal to the set terminal of the flip-flop circuit when the battery is connected to the RAM via the backup power supply circuit, and the signal is output from the flip-flop circuit. Next, when the ignition switch is turned on, the reset signal output means outputs a reset signal to the reset terminal of the flip-flop circuit after a predetermined time delay after turning on the power to the microcomputer, and the output of the flip-flop circuit is stopped. . Therefore, the signal is being transmitted from the flip-flop circuit within the predetermined time period from the time when the microcomputer is powered on for the first time after the power supply to the memory backup device is resumed, and after that, the signal transmission is stopped, so that the signal is not transmitted for the second time. When the microcomputer is powered on thereafter, the signal will not be transmitted.

In other words, when the microcomputer starts operating for the first time after power supply is resumed when the memory contents of the RAM are not correctly retained, the above-mentioned signal is transmitted.
The signal will not be transmitted when the microcomputer starts operating for the second time or later after the power supply is resumed, when the memory contents of the RAM are correctly maintained.
Therefore, if the above signal is detected when the microcomputer starts operating, it can be determined that the correct data is not stored in the RAM, and the microcomputer can operate accordingly. This prevents malfunctions based on

<Example> The present invention will be described below based on an example shown in FIG.

Configuration: In the figure, CPU 1, I/O (input/output signal processing unit) 2, ROM (read-only memory)
3 is supplied with power from a battery 4 via an ignition switch 5 and a power supply circuit 6, and RAM 7 is further supplied with power via a diode _D1 . Also, RAM
7 is supplied with power for memory backup, not through the ignition switch 5, but through a constant voltage backup power supply circuit 8 consisting of a Zener diode Z, a resistor _R, a capacitor C1 _, and a diode _D2 . ing. And these
The CPU 1, I/O 2, ROM 3, and RAM 7 exchange signals between each other via the bus 9, as in the prior art.

Here, the power supply restart signal output means is a resistor.
Consisting of R ₃ , R ₄ , diode D ₄ , capacitor C ₄ , and inverter 10, diode D ₃ and resistor
The battery voltage branched from before R ₂ is connected to resistors R ₃ and R ₄
The divided voltage is input to the inverter 10, and a diode D ₄ and a capacitor C ₂ are connected in parallel to the resistors R ₃ and R ₄ , respectively.
The time constants for the rise and fall of the voltage input to this inverter 10 are set. The output of this inverter 10 is the flip-flop circuit 11.
It is designed to be input to the set terminal 11a of the.

The flip-flop circuit 11 is a known RS flip-flop circuit using two NOR gates 11b and 11c, and the terminal voltage of the capacitor _C3 charged from the power supply circuit 6 via the resistor _R5 is input to the reset terminal 11d. It is becoming more and more common. The output terminal 11e is connected to I/O2 of the microcomputer.

The power supply circuit 6 starts supplying power to the CPU 1, I/O 2, and ROM 3 by turning on the ignition switch 5, and after a delay of about 100 milliseconds, starts supplying power for reset. Here, the reset signal output means consists of a power supply circuit 6, _a resistor _R5 , and a capacitor _{C3 .}
The time constant determined by the value of is selected so that the voltage at the reset terminal 11d of the flip-flop circuit 11 reaches the reset voltage when a predetermined time has elapsed after the microcomputer was powered on.

The CPU 1 is equipped with a signal detection means for detecting whether the output voltage of the flip-flop circuit 11 is at a high level or a low level until the predetermined time period elapses after the power is turned on.

Note that power is supplied to the inverter 10 and the flip-flop circuit 11 via the backup power supply circuit 8.

Action Next, a time chart (shown in Figure 2) showing changes in voltage at each point indicated by lowercase letters in Figure 1.
The effect will be explained with reference to.

After the in-vehicle microcomputer unit is removed from the vehicle, it is reattached to the vehicle and the battery is removed.
When the power supply to the memory backup device is stopped and then restarted, the voltage at point a in Figure 1 will be the same as when battery 4 is connected, as shown in Figure 2 A. At the same time, it becomes equal to the battery voltage, and this state continues until the battery 4 is removed again.

With this restart of power supply, the backup power supply circuit 8
A predetermined constant voltage is applied to the inverter 10, the flip-flop circuit 11, and the RAM 7 via the inverter 10, the flip-flop circuit 11, and the RAM 7. As shown in FIG. 2B, the voltage applied to the inverter 10 and the flip-flop circuit 11 reaches a predetermined voltage value after a certain delay time has elapsed after the power supply is restarted, and these two circuits become operational.

On the other hand, the battery voltage is divided by resistors R ₃ and R ₄ to charge capacitor C ₂ . this capacitor
The terminal voltage of C ₂ , that is, the voltage at point b in Figure 1 is:
As shown in FIG. 2C, the voltage increases with a time constant determined by resistors R ₃ and R ₄ and capacitor C ₂ and is input to the inverter 10. Output of inverter 10,
That is, the voltage at point C in FIG. 1 becomes high level as soon as power supply starts, setting the flip-flop circuit 11, as shown in FIG. 2 D, and then becomes low level when the input voltage, that is, the voltage at point b exceeds the operating voltage. .

The voltage at point d in FIG. 1, which is the output of the flip-flop circuit 11, becomes high level almost at the same time as the power supply is resumed, as shown in FIG. 2E, and is input to the I/O2. Here, when the ignition switch 5 is turned on, the power supply circuit 6 first starts supplying power to the microcomputer, then after a delay of about 100 milliseconds, the power is supplied to the capacitor via the resistor _R5 .
Start charging _C3 (see Figure 2 F and G).

As a result, the reset terminal voltage of the flip-flop circuit 11, that is, the voltage at point e in FIG. 1, increases with a time constant determined by the resistor _R5 and the capacitor _C3 , as shown in FIG. When the reset voltage is reached, the flip-flop circuit 11 is reset (see FIG. 2E) and its output is set to a low level.

In other words, the predetermined time after the ignition switch is turned on for the first microcomputer operation after power supply is resumed (the time indicated by T ₁ in Figure 2).
In this case, the output voltage of the flip-flop circuit 11 is at a high level. On the other hand, the output voltage of the flip-flop circuit 11 within a predetermined time (time indicated by T2 in FIG. 2) after the ignition switch ₅ is turned on for the second and subsequent microcomputer operation after power supply is resumed is already the same as the first one. Since it has been reset by turning the ignition switch 5 on, this state will continue until it is rolled.

With this restart of power supply, the backup power supply circuit 8
A predetermined constant voltage is applied to the inverter 10, the flip-flop circuit 11, and the RAM 7 via the inverter 10, the flip-flop circuit 11, and the RAM 7. As shown in FIG. 2B, the voltage applied to the inverter 10 and the flip-flop circuit 11 reaches a predetermined voltage value after a certain delay time has elapsed after the power supply is restarted, and these two circuits become operational.

On the other hand, the battery voltage is divided by resistors R ₃ and R ₄ to charge capacitor C ₂ . this capacitor
The terminal voltage of C ₂ , that is, the voltage at point b in Figure 1 is:
As shown in FIG. 2C, the voltage increases with a time constant determined by resistors R ₃ and R ₄ and capacitor C ₂ and is input to the inverter 10. Output of inverter 10,
That is, the voltage at point C in FIG. 1 becomes high level as soon as power supply starts, setting the flip-flop circuit 11, as shown in FIG. 2 D, and then becomes low level when the input voltage, that is, the voltage at point b exceeds the operating voltage. .

The voltage at point d in FIG. 1, which is the output of the flip-flop circuit 11, becomes high level almost at the same time as the power supply is resumed, as shown in FIG. 2E, and is input to the I/O2. Here, when the ignition switch 5 is turned on, the power supply circuit 6 first starts supplying power to the microcomputer, then after a delay of about 100 milliseconds, the power is supplied to the capacitor via the resistor _R5 .
Start charging _C3 (see Figure 2 F and G).

As a result, the reset terminal voltage of the flip-flop circuit 11, that is, the voltage at point e in FIG. 1, increases with a time constant determined by the resistor _R5 and the capacitor _C3 , as shown in FIG. When the reset voltage is reached, the flip-flop circuit 11 is reset (see FIG. 2E) and its output is set to a low level.

In other words, the predetermined time after the ignition switch is turned on for the first microcomputer operation after power supply is resumed (the time indicated by T ₁ in Figure 2).
In this case, the output voltage of the flip-flop circuit 11 is at a high level. On the other hand, the output voltage of the flip-flop circuit 11 within a predetermined time (time indicated by T2 in FIG. 2) after the ignition switch ₅ is turned on for the second and subsequent microcomputer operation after power supply is resumed is already the same as the first one. Since it has been reset by turning the ignition switch 5 on, it becomes low level.

Here, after the ignition switch is turned on, the predetermined time (time indicated by T ₁ and T ₂ in FIG. 2)
During this period, the output voltage of the flip-flop circuit 11 is detected by the signal detection means of the CPU 1, and if it is at a high level, the memory contents of the RAM have been destroyed, and on the other hand, if it is at a low level, the memory contents of the RAM have not been destroyed. It can be determined that there is no.

If it is determined that the RAM memory contents have been destroyed, the microcomputer will
Since the device operates by setting a new initial value without using the data in RAM as the initial value, malfunctions due to incorrect data are prevented.

In this embodiment, the necessary means are constituted by electric circuits, but these means may be constituted by a second microcomputer operated by a program stored in a non-volatile memory.

<Effects> As explained above, in the present invention, the backup confirmation device is configured to emit a signal if the memory contents of the RAM are destroyed when the in-vehicle microcomputer is powered on, so this signal can be detected. It becomes possible to take appropriate measures, prevent the on-vehicle microcomputer from operating based on erroneous data, and ensure reliable computer control.

Furthermore, since the circuit configuration is based on a flip-flop circuit, there is no malfunction due to vehicle vibration, and the reliability of the backup confirmation device is high. Furthermore, when the power is turned on to the microcomputer, the reset signal output means reliably delays the input of the signal to the reset terminal than the input of the signal to the set terminal, thereby preventing the flip-flop circuit from operating in an unstable manner. At the same time, the signal detection means can reliably detect the output voltage of the flip-flop circuit within a predetermined time, improving the reliability of the backup confirmation device.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
Figures A to H are time charts showing changes in voltage or state at each point shown in Figure 1, respectively. 1...CPU, 2...I/O, 3...ROM, 4...Battery, 6...Power supply circuit, 7...RAM, 8...Backup power supply circuit, 10...Inverter, 11...Flip-flop circuit, _R5 ...Resistor, _C3 ... capacitor.

Claims (1)

[Claims] 1 In an on-vehicle microcomputer that has a memory backup device that retains data by supplying power to the microcomputer's RAM from a battery via a backup power supply circuit, when a signal is input to the set terminal, a signal is output, and a signal is input to the reset terminal. Then, a flip-flop circuit stops outputting the signal, a power supply restart signal output means outputs a signal to a set terminal of the flip-flop circuit when the battery is connected to the RAM via the backup power supply circuit, and an ignition switch is turned on. reset signal output means for outputting a reset signal to a reset terminal of the flip-flop circuit after a predetermined time delay after power is turned on to the microcomputer; 1. A backup confirmation device for a memory backup device of a vehicle-mounted microcomputer, characterized in that the device has a signal detection means for detecting whether or not a signal is being transmitted at the same time.