JPH04320510A - Microcomputer resetting mechanism - Google Patents

Abstract

PURPOSE:To expand the holding period of the internal memory of a microcomputer and to prevent malfunction by sending a control signal for switching a reference voltage to a lower side by the microcomputer when the microcomputer receives an Acc OFF signal. CONSTITUTION:The microcomputer 21 when receiving the Acc OFF signal from an accessory(Acc) detecting circuit 13 outputs the reference control signal to a changeover switch 28. Thus, the changeover switch 28 can be switched to the reference voltage V2 for microcomputer stand-by 2V which is lower than an internal memory holding voltage in normal operation. Therefore, even if the voltage from a battery power source 17 drops temporarily for any reason in the stand-by mode of the microcomputer 21, a resetting circuit 16 does not output a reset signal. Consequently, the microcomputer 21 is not reset and the internal memory can securely be held.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a microcomputer reset mechanism, and more specifically, it is installed in in-vehicle audio equipment, etc., and uses a microcomputer whose memory retention voltage during microcomputer standby is set lower than the normal operating voltage. Regarding the microcomputer reset mechanism.

0002

[Prior Art] Generally, in car audio equipment,
When the user turns off Acc, that is, when the car is turned off, the equipment stops operating, the microcomputer performs appropriate processing, and then all power is turned off.
The consumption of battery power is kept low. However, at this time, only the microcomputer cannot turn off the power because it retains its internal memory, and enters microcomputer standby mode. This microcomputer standby mode is a low power consumption mode in which the power supply voltage of the microcomputer remains unchanged and power is consumed only for holding internal memory.

[0003] By the way, conventional in-vehicle audio equipment, etc. has a function such as clearing the internal memory of the microcomputer,
A microcomputer reset mechanism is provided for initialization. An example is shown in FIG. As shown in Figure 2, the microcomputer reset mechanism includes microcomputer 11 and microcomputer 1.
The reset circuit 16 includes a comparator 15 that compares the voltage from the battery power supply 17 with the microcomputer reset reference voltage V3.
is connected. A reset signal is output from the reset circuit 16 to the microcomputer 11 based on the comparison result from the comparator 15. Also A
The cc detection circuit 13 includes a comparator 13a whose + side of the input terminal is connected to the battery power supply 17 via the Acc switch 12, and whose - side is connected to the threshold voltage power supply 13b of about 7V. 13 shows the comparison results of each voltage, that is, Acc switch 1.
2 on/off detection signals are output to the microcomputer 11.

In the microcomputer reset mechanism configured as described above, a voltage of approximately 5 V is normally applied to the microcomputer 11 from the battery power source 17. For example, when the Acc switch 12 is on, a voltage of higher level than the Acc detection circuit 13 is applied. The signal is input to the microcomputer 11, and the microcomputer 11
operates while consuming normal power. Also Acc
When the switch 12 is turned off and a low level signal is input to the microcomputer 11 from the Acc detection circuit 13, the microcomputer 11 enters microcomputer standby mode, enters a low power consumption mode, and stops its own operation. On the other hand, when the voltage of approximately 5V is no longer applied to the microcomputer 11, such as when replacing the battery, the microcomputer reset reference voltage V3 becomes higher than the voltage from the battery power supply 17, so the comparator 15 outputs a high-level signal. The reset circuit 16
Output to. Then, the reset circuit 16 outputs a reset signal to the microcomputer 11 based on the signal, thereby resetting the microcomputer and initializing the internal memory of the microcomputer 11.

[0005]

[Problem to be Solved by the Invention] However, the above-mentioned microcomputer reset reference voltage V3 is normally 4.0V during normal operation of the microcomputer and during standby mode.
Since the voltage is set to about V, if the voltage from the battery power supply 17 drops for some reason when the microcomputer is on standby, such as when starting a car engine, the microcomputer will be reset immediately and the internal memory will be erased when unnecessary. This had the problem of being initialized.

Furthermore, the memory retention voltage of the microcomputer 11 during microcomputer standby is 2 V from the normal operating voltage of 5 V.
There are some that are set as low as V, but since the microcomputer is reset at about 4 V, even if the memory retention voltage is set low, there is a possibility that it will be reset before the internal memory is retained. Ta.

The present invention has been made in view of these problems, and provides a microcomputer reset mechanism that can extend the retention period of the internal memory of a microcomputer and prevent malfunctions due to battery voltage drop, etc. It is intended to.

[0008]

[Means for Solving the Problems] In order to achieve the above object, a microcomputer reset mechanism according to the present invention is provided in an in-vehicle audio device, etc., and the memory retention voltage during microcomputer standby is set lower than the normal operating voltage. In a microcomputer reset mechanism using a microcomputer, the microcomputer includes a plurality of reference voltages for resetting the microcomputer, and when the microcomputer receives an Acc off signal from an Acc detection circuit, the microcomputer switches the reference voltage to a lower side. It is characterized by a signal being transmitted.

[0009]

[Function] According to the above configuration, a plurality of reference voltages are provided for resetting the microcomputer, and Acc from the Acc detection circuit is provided.
When the microcomputer receives an OFF signal, it transmits a control signal to switch the reference voltage to a lower side, so that the AC from the Acc detection circuit is
When the microcomputer receives the c-off signal and enters microcomputer standby mode, even if the battery voltage drops for some reason, such as when starting a car engine,
A comparator that compares the battery voltage with the reference voltage switched to the lower side outputs a low level signal to the reset circuit, and the reset circuit does not output a reset signal. Therefore, even if the battery voltage temporarily drops for some reason, the microcomputer will not be reset and the internal memory will be reliably retained.

0010

Embodiments Hereinafter, embodiments of the microcomputer reset mechanism according to the present invention will be described with reference to the drawings. Note that components having the same functions as those of the conventional example are given the same reference numerals. FIG. 1 is a block diagram schematically showing an embodiment of a microcomputer reset mechanism according to the present invention.
, comparator 25 and Acc detection circuit 13, as well as a plurality of reference voltages V1 and V2 for resetting the microcomputer.
It is equipped with For example, if the internal memory retention voltage of the microcomputer 21 is set to approximately 5V during normal operation and approximately 2V during microcomputer standby, V1 is the reference voltage for 5V during normal operation, and V2 is the reference voltage for 2V during microcomputer standby. is a reference voltage, and each reference voltage V1
, V2 are connected to the - side input terminal of the comparator 25 via a changeover switch 28. The changeover switch 28 is connected to the microcomputer 21, and the microcomputer 2
According to the reference voltage control signal sent from 1, the reference voltage V1 for 5V during normal operation and the reference voltage V2 for 2V during microcomputer standby are switched. The + side input terminal of the comparator 25 is connected to the battery power supply 17, and the output side of the comparator 25 is connected to the reset circuit 16. This comparator 25 compares the voltage from the battery power supply 17 with a reference voltage V1 for 5V during normal operation or a reference voltage V2 for 2V during microcontroller standby, and outputs the result to the reset circuit 16. circuit 16
As in the prior art, a reset signal is output to the microcomputer 21 based on the comparison result from the comparator 25.

On the other hand, the Acc detection circuit 13 includes a comparator 13a as in the conventional case.
The + side of the input terminal is connected to the battery power supply 17 via the Acc switch 12, and the - side is connected to the threshold voltage power supply 13b of about 7V. Then, the Acc detection circuit 13 outputs the comparison result of each voltage, that is, A
The on/off detection signal of the cc switch 12 is sent to the microcomputer 2.
1.

In the microcomputer reset mechanism configured as described above, a voltage of approximately 5 V is usually applied to the microcomputer 21 from the battery power supply 17, and for example, when the Acc switch 12 is on, a voltage of higher level than the Acc detection circuit 13 is applied. The signal is input to the microcomputer 21, and the microcomputer 21
operates while consuming normal power. In addition, the microcomputer 21 switches the reference voltage control signal based on the high level signal from the Acc detection circuit 13 using a switch 28.
output and switch to the reference voltage V1 side for 5V during normal operation. And the comparator 25 is connected to the battery power supply 1
The voltage from battery power supply 17 is compared with the reference voltage V1 for 5V during normal operation.
Since the reference voltage V1 for 5V during normal operation is set lower than the voltage from the comparator 25, the comparator 25 outputs a low level signal to the reset circuit 16. Therefore, the reset circuit 16 does not output a reset signal, and the microcomputer 21 is not reset, so that the internal memory is reliably held.

[0013] Also, the Acc switch 12 is turned off and the
A low level signal from the cc detection circuit 13 is sent to the microcomputer 21.
When input to the microcomputer 21, the microcomputer 21 enters microcomputer standby, enters a low power consumption mode, and stops its own operation. Furthermore, the microcomputer 21 has an Acc detection circuit 13.
A reference voltage control signal is output to the changeover switch 28 based on the low level signal from the microcomputer standby, and the reference voltage is switched to the 2V reference voltage V2 side during microcomputer standby. The comparator 25 then compares the voltage from the battery power supply 17 with the reference voltage V2 for 2V during microcomputer standby, but similarly to the above, the reference voltage V2 for 2V during microcomputer standby is set lower than the voltage from the battery power supply 17. Therefore, the comparator 25 outputs a low level signal to the reset circuit 16. Therefore, the reset circuit 16 does not output a reset signal, and the microcomputer 21 is not reset, so that the internal memory is reliably held.

In this manner, during microcomputer standby, the reference control signal is output from the microcomputer 21 to the selector switch 28, and the selector switch 28 selects the reference voltage V2 for 2V during microcomputer standby, which is lower than the internal memory retention voltage during normal operation. Since it can be switched to the side,
When the microcomputer is on standby, even if the voltage from the battery power supply 17 drops for some reason, such as when starting a car engine, a low level signal is output from the comparator 25 to the reset circuit 16, and the reset circuit 16
No reset signal is output from. Therefore, even if the voltage from the battery power supply 17 temporarily drops for some reason, the microcomputer will not be reset and the internal memory will be reliably retained.

On the other hand, when the voltage of approximately 5V is no longer applied to the microcomputer 21, such as when replacing the battery, the reference voltage V2 for 2V during microcomputer standby becomes higher than the voltage from the battery power supply 17, so the comparator The terminal 15 outputs a high level signal to the reset circuit 16. Then, the reset circuit 16 outputs a reset signal to the microcomputer 11 based on the signal, thereby resetting the microcomputer and initializing the internal memory of the microcomputer 11.

As described above, in the microcomputer reset mechanism according to this embodiment, the Acc from the Acc detection circuit 13
When the microcomputer 21 receives the off signal, the microcomputer 21
The reference voltage control signal is switched from switch 28 to
Since the changeover switch 28 is switched to the reference voltage V2 for 2V during microcomputer standby, which is lower than the internal memory retention voltage during normal operation, the voltage from the battery power supply 17 may temporarily drop for some reason during microcomputer standby. Even if something happens, the microcomputer will not need to be reset, and the internal memory can be reliably retained. Therefore, the internal memory retention time is extended, and malfunction of the microcomputer reset mechanism due to a drop in the voltage of the battery power source 17 can be prevented.

[0017]

As described in detail above, the microcomputer reset mechanism according to the present invention includes a plurality of reference voltages for resetting the microcomputer, and when the microcomputer receives an Acc off signal from the Acc detection circuit, the microcomputer reset mechanism according to the present invention Since a control signal is sent to switch the reference voltage to a lower side, even if the battery voltage temporarily drops for some reason during microcomputer standby, the microcomputer will not be reset and the internal memory will be saved. Can be held securely. Therefore, the internal memory retention time can be extended, and malfunction of the microcomputer reset mechanism due to a drop in battery voltage or the like can be prevented.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram schematically showing an embodiment of a microcomputer reset mechanism according to the present invention.

FIG. 2 is a configuration diagram schematically showing an embodiment of a conventional microcomputer reset mechanism.

[Explanation of symbols]

13 Acc detection circuit 21 Microcomputer

Claims (1)

[Claims] [Claim 1] Disposed in in-vehicle audio equipment, etc.,
In a microcomputer reset mechanism using a microcomputer whose memory retention voltage during microcomputer standby is set lower than the normal operating voltage, there are multiple reference voltages for microcomputer reset, and Acc from the accessory (Acc) detection circuit is provided.
A microcomputer reset mechanism characterized in that when the microcomputer receives an OFF signal, the microcomputer transmits a control signal for switching the reference voltage to a lower side.