JPH11202980A - Circuit for rewriting and rewriting and erasing method for microcomputer having built-in flash memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide tolerance of disturbing noise and to securely control the rewriting and erasure of the flash memory. SOLUTION: The output port 31 of a reset IC 3 is connected to the reset port 2 of a microcomputer(MCU) 1 having the flash memory inside. To the input port 32 of the reset IC 3, a source voltage is applied through a resistance R1. Further, a connector 4 for reset signal input is connected to the input port 32 of the reset IC 3 through a resistance R2. The resistances R1 and R2 are so adjusted (e.g. R1=R2) that when 0 V is applied to the connector 4, the voltage applied to the input port 32 of the reset IC 3 is held between 0.65 to 4.25 V.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a rewriting circuit and a rewriting / erasing method for a microcomputer having a built-in erasable flash memory.

[0002]

2. Description of the Related Art A microcomputer (hereinafter, referred to as "MCU") having a built-in flash memory which can be electrically rewritten and erased is known. This MCU has an advantage that data such as a program stored in a built-in flash memory can be rewritten even after a product is mounted on a printed circuit board. For this reason, the MCU is employed in a control circuit of, for example, an air conditioner.

In order to rewrite data in the flash memory of the MCU, a rewriting circuit is required.
This rewriting circuit is also mounted on a printed circuit board on which is mounted. FIG. 1 shows a configuration example of a conventional rewriting circuit. In FIG. 1, the MCU 1 has a built-in flash memory that can be electrically rewritten and erased. Also MCU
1 is provided with a reset port 2 used for rewriting / erasing data in a built-in flash memory.
As a circuit for rewriting / erasing data in the flash memory, a rewriting circuit including a reset IC 3 and a rewriting jig connection connector 4 is provided. The rewriting circuit is mounted on a printed circuit board, similarly to the MCU1.

When rewriting or erasing data in the flash memory built in the MCU 1,
A jig (not shown) is connected to the connector 4, and 0 V is applied to the reset terminal of the connector 4. As a result, a low level (0 V) is applied to the reset port 2 of the MCU 1 via the wiring (pattern) 5, and data can be written / erased in the flash memory.

However, in such a rewriting circuit, the wiring (pattern) 5 sometimes functions as an antenna.
Disturbance noise is picked up by the wiring (pattern) 5,
There is a problem that the resistance of the MCU 1 to disturbance noise is weakened. As a countermeasure against such a problem, it is conceivable to eliminate the above-mentioned wiring (pattern) 5 and to provide a wiring (pattern) 6 extending from the reset terminal of the connector 4 to the input port of the reset IC 3 as shown by a broken line.

However, in this case, the output of the reset IC 3 becomes unstable, and a new problem that rewrite control cannot be performed is encountered. This is because the reset IC 3 generally has the characteristics shown in the operation waveform diagram of FIG. As shown in FIG. 2, the output state of the reset IC 3 is undefined when the voltage applied to the input port is 0.65 V or less. For this reason, even when 0 V is sent from the connector 4 to the input port of the reset IC 3 via the wiring (pattern) 6 shown in FIG.
The output of No. 3 is undefined, and there is no guarantee that the reset port of MCU 1 is kept at a low level, and data rewriting or erasing of the flash memory cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a rewriting circuit and a rewriting / erasing method which solve the above-mentioned problems, have resistance to disturbance noise, and can reliably control rewriting / erasing of a flash memory. .

[0008]

According to the first aspect of the present invention,
A rewriting circuit for a microcomputer having a built-in flash memory capable of electrically writing / erasing,
The microcomputer has an input port and an output port, a power supply voltage is applied to the input port, and the output port has a reset IC connected to the reset port of the microcomputer and a reset signal input connected to the input port of the reset IC. It is characterized by including a connector and a predetermined resistance element inserted between the input port of the reset IC and the connector.

According to the above configuration, the signal given from the reset signal input connector to the input port of the reset IC is given via the predetermined resistance element. Therefore,
When the voltage applied from the connector is at a low level, for example, 0
Even when the voltage becomes V, the voltage at the input port of the reset IC does not drop to 0 V due to the presence of the predetermined resistance element, and the state where a predetermined low voltage other than 0 V is applied is maintained.

According to a second aspect of the present invention, in the rewriting circuit according to the first aspect, the reset IC derives a high level output when a voltage applied to an input port is equal to or higher than a predetermined high threshold. When the voltage applied to the input port is between the high threshold value and a predetermined low threshold value, a low-level output is derived, and the output is undefined below the low threshold value. The inserted predetermined resistance element has a value such that a voltage between the low threshold value and the high threshold value is applied to an input port when a voltage of 0 V is applied to the connector. It is characterized by being set.

According to the above configuration, even if the characteristics of the reset IC are such that the output becomes indefinite when the voltage applied to the input port is 0 V, the reset IC is reset by a predetermined resistance element.
The input port of C is maintained at a predetermined low voltage other than 0V. Therefore, the output of the reset IC does not become unstable, and the output of the reset IC can be controlled to a high level or a low level.

According to a third aspect of the present invention, there is provided a rewriting / erasing method for a microcomputer having a flash memory capable of electrically rewriting / erasing, wherein an output port of a reset IC having an input port and an output port is provided. A reset IC connected to a reset port of the microcomputer for rewriting or erasing data in a flash memory built in the microcomputer.
A 0V voltage is applied to the input port through a predetermined resistor.

According to the above configuration, a 0 V voltage is applied to the input port of the reset IC through a predetermined resistor.
The output voltage of the reset IC can be reliably controlled, and data in the flash memory can be rewritten and erased satisfactorily.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. FIG.
1 is a circuit diagram showing an MCU 1 having a built-in flash memory capable of electrically rewriting and erasing data, and a data rewriting circuit of the flash memory. In this circuit, reset IC3 is connected to reset port 2 of MCU1.
Output port 31 is connected. Reset IC
3 input port 32 is connected to a power supply voltage of 5 V through a resistor R1.
Is applied. Further, a reset signal input connector 4 is connected to the input port 32 of the reset IC 3 via a resistor R2.

In this circuit, the reset IC 3 has the characteristics shown in the operation waveform diagram of FIG. That is, when the voltage applied to the input port 32 is 4.25 V or more, the output is at a high level, and when the voltage applied to the input port 32 is 0.65 V or more and less than 4.25 V, the output is at a low level. Further, when the voltage applied to the input port 32 is 0.6
If it is less than 5 V, the output will be undefined.

Therefore, in the circuit of FIG. 3, when the voltage applied from the connector 4 becomes 0 V, the applied voltage V _IN to the input port 32 of the reset IC 3 becomes 0.65 V ≦ V _IN <
The values of the resistors R1 and R2 are adjusted to be 4.25V. As an example, the values of the resistors R1 and R2 are set to, for example, R1 = R2. In this way, when a low signal (0 V) is sent from the rewriting jig through the connector 4, the circuit of FIG. 3 becomes an equivalent circuit shown in FIG. 5V
Is applied. Therefore, a low level signal is output from the output port 31 of the reset IC, and the reset port 2 of the MCU 1 is kept at a low level.

On the other hand, when a high level signal (5 V) is sent from the rewriting jig through the connector 4, the circuit shown in FIG. 3 becomes an equivalent circuit shown in FIG. In this case, since 5 V is applied to the input port 32 of the reset IC 3,
A high-level signal is derived from the output port 31 of the reset IC 3. Therefore, a high level signal is given to the reset port 2 of the MCU 1. Similarly, when the rewriting jig is removed, the connector 4 is opened, and FIG.
Is an equivalent circuit shown in FIG. 6, and a high-level signal is supplied to the reset port 2 of the MCU 1.

Therefore, in the case of the circuit shown in FIG. 5 and the circuit shown in FIG. 6, the data in the flash memory incorporated in the MCU 1 cannot be rewritten or erased.

[0019]

According to the present invention, the wiring (pattern) for writing data to the flash memory built in the MCU and erasing the written data is connected to the power supply side of the reset IC via the resistor. As a result, the wiring (pattern) 5 connected to the reset port of the MCU 1 which has been required conventionally can be eliminated. Therefore, since there is no wiring (pattern) 5 acting as an antenna,
The circuit can be made more resistant to disturbance noise,
It is possible to provide a configuration in which the MCU does not easily malfunction.

Further, a signal for writing / erasing data to / from the flash memory can be reliably sent to the MCU, and a rewriting circuit and method excellent in rewriting control of the flash memory can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a conventional flash memory rewriting circuit.

FIG. 2 is an operation waveform diagram showing general characteristics of a reset IC.

FIG. 3 is a diagram showing a configuration of a flash memory rewriting circuit according to one embodiment of the present invention;

FIG. 4 is an equivalent circuit diagram at the time of rewriting the flash memory in the circuit of FIG. 3;

FIG. 5 is an equivalent circuit diagram showing a signal state when rewriting is not performed in the circuit of FIG. 3;

FIG. 6 is an equivalent circuit diagram when a rewriting jig is not connected to the circuit of FIG. 3;

[Explanation of symbols]

Reference Signs List 1 MCU (microcomputer with built-in flash memory) 2 Reset port of MCU 3 Reset IC 31 Output port of reset IC 32 Input port of reset IC 4 Connector for reset signal input 5 Wiring (pattern) 6 Wiring (pattern) R1, R2 resistance

Claims (3)

[Claims] 1. A rewriting circuit for a microcomputer (1) incorporating a flash memory capable of electrically writing and erasing, comprising an input port (32) and an output port (31).
A power supply voltage is applied to an input port (32), an output port (31) is a reset IC (3) connected to a reset port (2) of the microcomputer (1), and an input port of the reset IC (3). A reset signal input connector (4) connected to (32), a predetermined resistance element (R2) inserted between the input port (32) of the reset IC (3) and the connector (4); A rewriting circuit, comprising: 2. The rewriting circuit according to claim 1, wherein said reset IC (3) derives a high-level output when a voltage applied to said input port (32) is equal to or higher than a predetermined high threshold. A low-level output is derived when the voltage applied to the input port (32) is between the high threshold value and a predetermined low threshold value, and the output is indeterminate below the low threshold value. Wherein the inserted predetermined resistance element (R2) receives a voltage between the low threshold value and the high threshold value when a 0V voltage is applied to the connector (4). Port (32)
A rewriting circuit characterized in that the value is set to a value applied to the rewriting circuit. 3. A rewriting / erasing method for a microcomputer (1) having a flash memory capable of electrically rewriting / erasing, comprising: a reset IC having an input port (32) and an output port (31). 3) The output port (31) of the microcomputer (1) is connected to the reset port (2) of the microcomputer (1), and the reset IC is used to rewrite or erase data in the flash memory built in the microcomputer (1). A predetermined resistance (R) is connected to the input port (32) of (3).
A method characterized in that a 0V voltage is applied through 2).