JPH0738990Y2 - Voltage drop detection circuit for electronic devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an electronic device having a microcomputer and a backup power supply circuit for memory protection, and more particularly to a voltage drop detection circuit for a backup power supply of in-vehicle electronic devices.

[Prior art]

2. Description of the Related Art In recent years, many electronic control devices have been developed that electronically control an engine, a transmission, or the like in order to satisfy requirements for cleaning exhaust gas, saving energy, or improving driving performance for automobiles and the like. In these electronic control devices, a microcomputer is generally used as the control becomes complicated. For example, in a fuel injection device, engine operation information detected by various sensors is processed by a microcomputer to control the fuel injection amount, injection timing and the like.

Such an electronic control unit usually operates only when the ignition switch of the car is turned on, but even when the ignition switch is turned off, if it is necessary to protect the contents of the memory (RAM), the power supply of the RAM, Alternatively, in the case of a one-chip microcomputer (CPU), the power of the CPU is supplied directly from the battery without passing through the ignition switch (this power supply is called the backup power supply). Examples of the contents written in the RAM protected in this manner include self-diagnosis result data, correction data for correcting the mounting error of the sensor for detecting the position of the movable portion, and the like.

In the case of an electronic control unit that has a RAM that is backed up in this way, is the data read from the RAM correctly written data, or is it data in an unstable state immediately after the battery is first connected? To distinguish
In the latter case, it is necessary to write initial data and initialize it. FIG. 3 is a diagram showing a configuration of a conventional voltage drop detection circuit for determining whether the battery is continuously connected or has a history of being once removed.

In the figure, 21 is a backup power input terminal,
When the backup power supply (battery) is first connected to this backup power supply input terminal 21 when the CPU does not connect the normal power supply by the ignition switch, the time constant circuit 26 (composed of the resistor R and the capacitor C) ) Sets the flip-flop 22 and outputs 25
Becomes H (high) level. After this, the ignition switch (not shown) is turned on and the regular power supply is connected to CPU2.
When 3 starts operating, check the above output 25,
If 5 is H level, backup power supply (battery)
Is determined to be the state immediately after being connected to the backup power input terminal 21, and the contents of the backup RAM are indefinite, so the backup RAM is initialized and the flip-flop is prepared for the next ignition switch ON.
The reset signal is output to the reset terminal 24 of 22. That is,
If the output 25 is at H level when the CPU starts operating, the backup power supply (battery) that is the power supply for RAM
Is determined to have been connected to the backup power supply input terminal 21, and the fact that this backup power supply was connected means that the backup power supply was not connected before that, and the contents of the backup RAM were destroyed. Backup RA
The contents of M are initialized, and then a reset signal is output to the reset terminal 24 of the flip-flop 22 to indicate that it is not necessary to initialize again, and the output is set to L (low) level. If the output 25 is at the L level when the CPU starts operating, it is determined that the contents of the backup RAM have been destroyed and the backup RAM is not initialized. CPU23 of this part
FIG. 4 shows an operation flowchart of the above.

That is, it is judged whether the output of the flip-flop 22 is at the H level by turning on the power (turning the ignition switch on and turning on the regular power) (step 201). If the output is at the H level, the backup RAM is initialized (step 202) and the flip-flop is turned on. The reset signal is output to the reset terminal 24 of the amplifier 22.

[Problems to be solved by the device]

However, in the voltage drop detection circuit shown in FIG.
Although the reset terminal 24 of the flip-flop 22 is used only under extremely limited conditions, it must be provided as an independent output port of the CPU 23, increasing the number of output ports of the CPU 23 and eventually increasing the size of the device. , Leading to higher prices. Further, the flip-flop 22 is often configured as a single power supply control IC together with a voltage regulator for the power supply of the CPU 23, but there is also a problem that the number of pins of this power supply control IC increases.

The present invention has been made in view of the above points, and an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a small-sized, low-cost voltage drop detection circuit for electronic devices.

[Means for Solving the Problems]

In order to solve the above problems, the present invention provides a CPU, a RAM, and a RAM.
It is equipped with a backup power supply that protects the contents of, and a flip-flop that is set when the backup power supply is connected to RAM.
In the voltage drop detection circuit of the electronic device that determines whether to initialize the RAM when the operation of the CPU is started, the reset signal of the flip-flop is also used as the reset signal of the watchdog timer.

[Action]

By configuring the voltage drop detection circuit as described above, the reset signal of the watchdog timer is also used as the reset signal of the flip-flop, so that the number of output ports of the CPU is not increased and the power regulator of the flip-flop and the CPU is not increased. Even when these are configured as a single power supply control IC, the number of pins of the power supply control IC does not increase.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a voltage drop detection circuit of an electronic device according to the present invention. In the figure, 1 is a backup power input terminal, 2 is a flip-flop, 3 is a CPU, 4 is a reset signal of the watchdog timer 7 and a reset signal of the flip-flop 2, 5 is an output signal of the flip-flop 2, and 6 is a time. A constant circuit (composed of a resistor R and a capacitor C), 8 is an output signal of a watchdog timer 7 which resets the CPU 3 when the CPU 3 runs out of control. In the voltage drop detection circuit of FIG. 1, the same as the voltage drop detection circuit of FIG. 3 from the first connection of the power supply to the backup power supply input terminal 1 until the output signal 5 of the flip-flop 2 becomes H level. Is. After that, when the ignition switch (not shown) is turned on and the CPU 3 starts operating, normally, it immediately starts outputting the reset signal to the watchdog timer 7, but in the present invention, the first reset signal is output. The output signal 5 of the flip-flop 2 is checked before, and after confirming this, a reset signal is output to the watchdog timer 7. A flowchart in this case is shown in FIG.

In FIG. 2, the output signal 5 of the flip-flop 2 is H
It is judged whether or not it is the level (step 101), and when it is the H level, the reset signal 4 of the watchdog timer 7 and the reset signal 4 of the flip-flop 2 are output to reset the flip-flop 2 and then the backup RAM. Is initialized (step 103). Backup when the output signal 5 of the flip-flop 2 is not at H level
Do not initialize the RAM and proceed to the next step.

Since the reset signal for resetting the watchdog timer 7 from the CPU 3 is also used as the flip-flop reset signal as described above, it is necessary to provide the output port of the CPU 3 with a single output port for resetting the flip-flop 2. Disappear.

[Effect of device]

As described above, according to the present invention, since the reset of the watchdog timer and the reset of the flip-flop are performed by the same port of the computer, the following excellent effects can be obtained.

The number of computer ports can be reduced, and miniaturization and cost reduction can be expected.

Software is simplified because no special processing for resetting the flip-flop is required.

When the flip-flop is configured as a single power supply control IC together with a computer power supply regulator, a watchdog timer, etc., the number of pins of this power supply control IC can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a voltage drop detection circuit of an electronic device according to the present invention, FIG. 2 is an operation flowchart of a CPU of FIG. 1, and FIG. 3 is a configuration of a voltage drop detection circuit of a conventional electronic device. FIG. 4 and FIG. 4 are operation flowcharts of the CPU of FIG. In the figure, 1 ... Backup power input terminal, 2 ... Flip-flop, 3 ... CPU, 4 ... Reset signal and flip-flop signal, 5 ... Output signal, 6 ... Time constant circuit,
7: Watchdog timer, 8: Output signal.

Claims (1)

[Scope of utility model registration request] 1. A CPU, a RAM, a backup power supply for protecting the contents of the RAM, and a flip-flop that is set in response to the backup power supply being connected to the RAM, and the output of the flip-flop. In a voltage drop detection circuit of an electronic device that determines whether to initialize the RAM at the start of operation of the CPU according to, a reset signal of the flip-flop is also used as a reset signal of a watchdog timer. Voltage drop detection circuit for electronic equipment.