JPH0237063Y2 - - Google Patents

Description

[Detailed Description of the Invention] (A) Field of Industrial Application The present invention relates to a startup circuit in an electronic circuit device using a microcomputer, and particularly to a startup circuit for a microcomputer having a hold function.

(b) Prior Art Generally, when operating a device such as a microcomputer, the microcomputer is initialized by a reset signal generated when the power supply voltage is turned on. For devices such as these that completely shut off the power with a power switch or devices that use commercial power, initial settings are always made when the power is turned on or when recovering from a power outage, etc., so the previous operation will be changed. The stored data will be deleted. Therefore, for devices that need to retain data, as in Japanese Utility Model Publication No. 57-12438, the device can be operated continuously by backing up in the event of a power outage or by constantly supplying power with a battery. It holds data. However, if the device is operated all the time, it increases power consumption and shortens battery life, so a microcomputer with a hold function is used in such a device.

The hold function is a function of stopping the operation of internal circuits including the oscillation circuit by applying a hold signal of a predetermined level of potential, for example, ground potential "0" to the hold terminal. That is,
When a hold signal is applied, the microcomputer enters the hold state after the currently executed instruction is completed, stops the oscillation circuit, resets the interrupt flag and timer, and stops operation, but all registers are , memory, etc. are held in the state immediately before the hold state.

Therefore, when there is no need to operate, a switch or the like can be used to apply "0" to the hold terminal to enter the hold state, and release the hold state as necessary. However, when connecting the power source (battery) for the first time, the microcomputer must be initialized, so when creating a reset signal, it is necessary to operate a switch etc. to release the hold state, and then reset the hold state again. You must perform an operation to bring it into the state. Therefore, there is a drawback that the operation becomes cumbersome when replacing the battery or the like.

(c) Purpose of the invention The present invention has been made in view of the above-mentioned points, and provides a startup circuit for a microcomputer that automatically performs initial settings and then automatically enters a hold state when power is applied. The purpose is to provide.

(d) Structure of the invention The invention provides a first circuit that operates when the power is turned on in a microcomputer startup circuit that has a hold function that stops the operation of the internal circuit when a signal of a predetermined level is applied to the hold terminal. a time constant circuit; switching means controlled by the first time constant circuit and applying a predetermined level to the hold terminal for a period determined by the first time constant circuit; a second time constant circuit that operates when applied and creates a reset signal with a time constant shorter than the time constant of the first time constant circuit; and a switch that forcibly applies a predetermined level to the hold terminal. , after turning on the power, release the hold state and perform initial settings within a period determined by the first time constant circuit, then return to the hold state, release the hold state by operating the switch, and start operation. This is the configuration to start.

(E) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention.
1 is a microcomputer, 2 is a battery, 3 is a first
4 is a second time constant circuit, 5 is a transistor, and 6 is a switch.

The power supply terminal V _DD of microcomputer 1 has
The positive potential of the detachably connected battery 2 is applied via the power supply line 7. The first time constant circuit 3 connected between the power supply line 7 and the ground includes a resistor R ₁ ,
R ₂ , a capacitor C ₁ and a diode D ₁ , and a voltage varying according to a time constant determined by the resistor R ₁ and the capacitor C ₁ is applied to the base of the transistor 5 via the resistor R ₂ . Ru. Also,
Diode D ₁ is for discharging the charge of capacitor C ₁ when battery 2 is removed.
The transistor 5 used as the switching means is of PNP type, and its emitter is connected to the power supply line 7, and its collector is connected to the diode D ₂ , the resistor R ₃ and the input terminal R/H of the microcomputer 1. The input terminal R/H is a terminal for determining whether or not to perform initial settings when the microcomputer 1 operates. The other terminal of the diode _D2 is connected to the hold terminal, and the second time constant circuit 4 is connected between the hold terminal and ground. The second time constant circuit 4 is a circuit for creating a reset signal, and is composed of resistors R ₄ and ₅ , a capacitor C ₂ and a diode D ₃ , and the time constant determined by the resistor R ₄ and capacitor C ₂ is as follows. The time constant is set smaller than the time constant of the first time constant circuit 3. The connection point between resistor _R4 and capacitor _C2 , whose voltage changes based on the time constant, is connected to the reset terminal, and the reset signal is sent to microcomputer 1.
is supplied to. Resistor R ₅ and diode D ₃ are
It forms the discharge path of capacitor _C2 ,
When the potential of the hold terminal reaches the ground level, the charge in the capacitor _C2 is discharged via the resistor _R5 , the diode _D3 , and the resistor _R6 . Also,
Between the hold terminal and power line 7,
Switch 6 and diode D ₄ are connected in series,
By closing switch 6, the hold terminal
The potential of HOLD is raised to the power supply voltage level. Further, one end of the switch 6 is connected to an input terminal HSW of the microcomputer 1 as information indicating whether the switch 6 is open or closed. Note that the resistor _R7 is a pull-down resistor for the input terminal HSW.

The operation of the starting circuit formed as shown in Fig. 1 is explained in the second section.
This will be explained with reference to the waveform diagram in the figure. First, when the battery 2 is first connected, a power supply voltage is applied to the power supply terminal _VDD . At this time, the potential at the connection point _VB between the resistor _R1 and the capacitor _C1 of the first time constant circuit 3 gradually increases according to the time constant, but for a while, the potential at the connection point VB increases.
The potential difference between V _B and the emitter of transistor 5 is
Since V _BE of transistor 5 is larger, transistor 5 is turned on at the same time as power is applied, raising the collector potential, that is, the potential of input terminal R/H to the power supply voltage level, and also raising the hold terminal to the power supply voltage via diode D ₂ . raise the level. Furthermore, at this time, a charging current flows through the capacitor _C2 of the second time constant circuit 4 via the transistor 5, the diode _D2 , and the resistor _R4 , and the potential applied to the reset terminal gradually increases.
However, since the time constant of the second time constant circuit 4 is smaller than that of the first time constant circuit 3, the time _T2 until the terminal reaches the operating level at which the reset is released is different from the connection point _VB. Time T ₁ until the voltage between emitters becomes smaller than V _BE of transistor 5
shorter. Therefore, the hold state of the microcomputer 1 is released by the hold terminal reaching the power supply voltage level, and the microcomputer 1 is reset during the time until the potential of the reset terminal reaches the operating level. It is. And the reset terminal
When the potential of RES reaches the operating level, the reset is released, and the microcomputer 1 starts operating and starts executing the program from address 0. This program first determines the information on the input terminal R/H and proceeds with the program based on that information. That is, in this case, transistor 5
Since the input terminal R/H is on, the input terminal R/H is at the power supply voltage level, and in this case, the initial setting program is executed and the internal RAM settings, input/output settings, etc. are performed.

Thereafter, when the potential difference between the connection point V _B and the emitter becomes smaller than V _BE of the transistor 5, the transistor 5 is turned off. As a result, the input terminal R/H is pulled down to the ground level by the resistor _R3 , and the potential of the hold terminal is also pulled down to the ground level by the resistor _R6 . On the other hand, the charge on capacitor C ₂ is divided by resistor R ₅ , diode D ₃ , resistor R ₆
Since the voltage is discharged through the reset terminal, the potential of the reset terminal is also lowered to the ground level. Therefore, the microcomputer 1 enters the hold state again and stops operating.

In this way, the microcomputer 1 is automatically reset and initialized when the battery 2 is connected, and then automatically enters the hold state. In this state, when operating the microcomputer 1, the switch 6 is closed. When switch 6 is closed, the power supply voltage is connected to diode D ₄
is applied to the hold terminal via the capacitor C ₂ of the second time constant circuit 4 from the battery 2 to the switch 6, the diode D ₄ and the resistor.
A charging current flows through _R4 , and the potential at the reset terminal gradually rises. Therefore, the hold state of the microcomputer 1 is released and the reset is performed within the time _T2 until the potential of the reset terminal reaches the operating level. And time T ₂
Thereafter, when the reset is released, the microcomputer 1 executes the program from address 0, as described above. In this case, the input terminal R/H is at the ground level because the diode D ₂ is reverse biased, and as a result of determining the input terminal R/H by the program, no initial setting is performed, and the input terminal
Make sure HSW is at supply voltage level,
Start execution of the main program. After the operation is completed, when the switch 6 is opened, the hold terminal and the reset terminal are pulled down to the ground level, and the operation is again brought into the hold state and stopped. When in this hold state, the contents of the RAM or registers of the microcomputer 1 are held, but the power consumption is very small.

FIG. 3 is a flow diagram of the first program executed by the microcomputer 1 after being released from reset, that is, the program started from address 0. In FIG. 3, first, data at input terminal R/H is input, and it is determined by a determination command whether or not the power supply voltage level is "1". If the result of the determination is "1", it means that the transistor 5 is on, that is, when the battery 2 is connected for the first time, so the initial setting is necessary to set the internal RAM, register, or input/output state to a predetermined value. Execute. After the initial settings are completed, input the data of the input terminal HSW and judge whether it is "1" or not. If the result of the judgment is "1", it means that switch 6 is closed, so start the main program. This is executed, but if it is not "1", the judgment command is repeated and the process waits until the hold state is reached. on the other hand,
If the determination result of the input terminal R/H is not "1", the transistor 5 is in the off state, that is, the battery 2
is already connected and initial settings should not be performed, so jump the initial settings program, judge the input terminal HSW,
After confirming that switch 6 is closed, execute the main program.

(f) Effects of the invention As described above, according to the invention, after the initial setting is automatically performed when power is applied, the system is automatically placed in the hold state, and the initial setting is not performed when the operation starts thereafter. This provides a startup circuit, and has the advantage of eliminating the hassle of operating a switch when starting the operation of a microcomputer.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of the circuit shown in FIG. 1, and FIG. 3 is a flow diagram showing the operation of the microcomputer. 1...Microcomputer, 2...Battery, 3
...First time constant circuit, 4...Second time constant circuit, 5...Transistor, 6...Switch.

Claims (1)

[Scope of utility model registration request] In a microcomputer startup circuit having a hold function that stops the operation of an internal circuit when a signal of a predetermined level is applied to a hold terminal, a first time constant circuit that operates when the power is turned on;
switching means that is controlled by the first time constant circuit and applies a predetermined level to the hold terminal for a period determined by the first time constant circuit; and a switching means that operates when the predetermined level is applied to the hold terminal. A second time constant circuit generates a reset signal using a time constant shorter than the time constant of the first time constant circuit, and a switch for forcibly applying a predetermined level to the hold terminal. 1
After the hold state is released and initial settings are performed within a period determined by the time constant circuit, the hold state is returned to the hold state, and the hold state is released and the operation is started by operating the switch. Microcomputer startup circuit.