GB2328094A

GB2328094A - Instantaneously detecting an abnormal voltage in a micro controller

Info

Publication number: GB2328094A
Application number: GB9716385A
Authority: GB
Inventors: Jason Chen; Yi Lin
Original assignee: Holtek Microelectronics Inc
Current assignee: Holtek Microelectronics Inc
Priority date: 1997-08-01
Filing date: 1997-08-01
Publication date: 1999-02-10
Also published as: GB9716385D0

Abstract

Disclosed is an apparatus for instantaneously detecting an abnormal voltage in a micro controller. The means mainly includes a detecting circuit for setting a voltage value to be detected and a latch circuit. The detecting circuit is a logic "NOT" gate which has a power supply connecting terminal connected to a reset voltage terminal of an internal circuit of the micro controller to be detected, an input terminal connected to a power supply terminal of the internal circuit of the micro controller, and an output terminal connected to a cooperating input terminal of the latch circuit. The output terminal of the latch circuit can output a flag signal reflecting an abnormal voltage in the micro controller. Thus whenever there is an instantaneous change of the micro controller's voltage to a non-nominal rating, the voltage change can be instantaneously detected and be latched by a signal, causing the flag signal output from the latch circuit to reflect an abnormal voltage for the micro controller to effect an instantaneous interrupt or reset.

Description

APPARATUS FOR INSTANTANEOUSLY DETECTING AN ABNORMAL VOLTAGE IN A MICRO CONTROLLER The present invention relates to an apparatus for instantaneously detecting an abnormal voltage in a micro controller, and more particularly to a digital circuit for instantaneously detecting a voltage of a micro controller, so that an instantaneous change of the voltage to a non-nominal rating can be detected and an abnormal voltage signal reflecting the change can be output as a basis for the micro controller to effect an instantaneous interrupt or reset.

A conventional micro controller can operate normally only within a certain range of supply voltage. Once the supply voltage exceeds the normal range, it will result in abnormal operation in the micro controller. Hence, recent protection design against the abnormal supply voltage which shall cause disorder of a micro controller must be able to reset the micro controller when it encounters an abnormal supply voltage, until the supply voltage becomes normal again. Then, the micro controller is re-started to work. Under this condition, it is necessary to provide voltage detecting means near the micro controller to screen the supply voltage.

In a generally designed voltage detecting means, as shown in Fig. 1A, a voltage detector comprising an analog circuit is employed. However, general micro controllers do not use such voltage detectors because the analog circuit structure is found not satisfactory for a system in which power-saving is a must. Figs. 1B and 1C illustrate other conventional voltage detecting means for micro controllers. As shown, the micro controller is provided with an external Reset pin for a user. Such Reset pin requires an external circuit which includes an RC low pass filter structure. Patent Application laid open on July 11, 1996 under number PCT WO 96/21158 discloses such structure. In this design, only when the supply voltage drops for a considerably long time will the voltage at the ResetO pin change with the supply voltage to generate a proper ResetO signal.

This is because the switching threshold of the inverter in Fig. 1B (which is designed to detect a drop in the supply voltage) will itself fall when the supply voltage falls. A similar effect occurs in the circuit of Fig. 1C, which is designed to detect a sudden increase in the supply voltage. In the event the supply voltage quickly drops from a stable state and then quickly comes up again, such instantaneous change shall still result in abnormal operation or even failure of the micro controller. In brief, the conventional voltage detecting means as shown in Figs. 1B and 1C cannot detect the instantaneous abnormal voltage and can be used to detect a voltage change and issue a Reset signal only when the voltage change lasts for a significant time interval. This is, of course, not an ideal structure, either.

The inventor has therefore tried to develop a means for instantaneously detecting abnormal voltage in a micro controller to eliminate the drawbacks existing in the conventional means for similar purpose.

A primary object of the present invention is to provide a means for instantaneously detecting abnormal voltage in a micro controller.

According to the invention, there is provided apparatus for instantaneously detecting an abnormal voltage in a micro controller, comprising a detecting circuit for setting a voltage value to be detected and a latch circuit, said detecting circuit being a logic "NOT" gate which has a power supply connecting terminal connected to a reset voltage terminal of an internal circuit of said micro controller, an input terminal connected to a power supply terminal of the internal circuit of said micro controller, and an output terminal connected to a cooperating input terminal of said latch circuit; and said latch circuit having an output terminal for outputting a flag signal reflecting an abnormal voltage in said micro controller; whereby whenever there is an instantaneous change of said micro controller's voltage to a non-nominal rating, said voltage change can be instantaneously detected and be latched by a signal, causing said flag signal output from said output terminal of said latch circuit to reflect an abnormal voltage for said micro controller to effect an instantaneous interrupt or reset.

The preferred embodiment includes a detecting circuit which does not use the micro controller's voltage power supply but uses a voltage at a Reset pin having the effect of a low pass filter as its power supply, lest an inaccurate instantaneous detecting result should be obtained due to a comparison point of the internal logic circuit varying with the supply voltage when the supply voltage suddenly drops.

Moreover, in the present invention a digital circuit is used to replace the conventional analog circuit and therefore reduces power consumption at the Reset pin and shortens the time interval of voltage change required by the detection.

The detailed structure, the applied principle, and the function and performance of the present invention can be best understood by referring to the following detailed description of a preferred embodiment, given by way of example only, and the accompanying drawings, wherein: Fig. 1A shows a conventional voltage detector including an analog circuit; Fig. 1B shows a conventional means for detecting abnormal voltage in a micro controller; Fig. 1C shows another conventional means for detecting abnormal voltage in a micro controller.

Fig. 2 is a logic circuit diagram of apparatus according to the present invention; and Fig. 3 is a graph showing the abnormal voltage detected by the means of the present invention.

The present invention relates to apparatus for instantaneously detecting an abnormal voltage in a micro controller. Please refer to Fig. 2 in which a logic circuit of an apparatus according to the present invention is shown. As shown, the apparatus includes a detecting circuit 1 for setting a voltage value to be detected and a latch circuit 2. The detecting circuit 1 has a logic "NOT" gate 10 which is preferably a CMOS.

The detecting level VDL can be determined by the sizes of the PMOS and NMOS transistors in the adjusted CMOS.

Moreover, said CMOS can be a Schmitt trigger with a transition point V1H1 and Viol. This logic "NOT" gate 10 has a power supply connecting terminal P1 leading to a reset voltage terminal (Vres) of an internal circuit of a micro controller to be detected as at the left-hand side of Fig. 1B, and an input terminal P2 connected to a power supply terminal (VDD) of the internal circuit of the micro controller to be detected. The logic "NOT" gate 10 also has a power failure detect output terminal (PFDO) connected to a cooperating input terminal P3 of the latch circuit 2. The latch circuit 2 may be a flipflop or a latch which is functionally equivalent to a flip-flop. As shown in the figure, when a flip-flop 11 is used as the latch circuit 2, a CB terminal of the flip-flop 11 is connected to the output terminal (PFDO) of the logic "NOT" gate 10, a D terminal a power supply connecting terminal P4 thereof are together connected to the reset voltage terminal (Vres) of the internal circuit of the above-mentioned micro controller to be detected. Output terminals Q and R of the latch circuit 2 can output power failure flag signals (PFF) reflecting a detected abnormal voltage. These flag signals (PFF) may be led to a reset circuit (to reset the micro controller) , or may be used to trigger a non-maskable interrupt, or be provided to a user only for his or her use and judgement of the abnormal condition. Hence, whenever there is an instantaneous change of the micro controller's voltage to a non-nominal rating, it can be instantaneously detected and be latched by a signal, causing the flag signal (PFF) at the output terminals of the latch circuit 2 to issue an abnormal voltage signal for the micro controller to effect an interrupt or to reset.

A detecting potential of the detecting circuit 1 can be set through a mask option to meet the requirements of the entire system in which the apparatus of the present invention is incorporated so that applications of the apparatus of the present invention can meet various needs.

In Figure 2, when CB is equal to clock low, it becomes a falling edge trigger and Q is equal to D; howver, during other times Q is not influenced by CB. On RESET"1" Q equals 0, otherwise Q is not influenced.

In Figure 1B, L3 is the signal of RESETO. V1H and V1L are the transition points of the Schmitt trigger in Fig. 1B.

This situation can be expressed by: When VRES > V1H, RESET0=0; when VRES < VlL, RESETO=1; otherwise RESETO remains the same.

Fig. 3 is a graph illustrating how the apparatus of the present invention functions when an abnormal voltage is present in the micro controller. In the drawing, line L1 is a voltage/time graph obtained at the abovementioned power supply terminal (VDD), curve L2 is a voltage/time curve obtained at the above-mentioned reset voltage terminal (Vres), line L3 is a voltage/time line obtained at the above-mentioned RESET0 output terminal, line L4 is a voltage/time line obtained at the power failure detector output (PFDO) terminal of the abovementioned logic "NOT" gate 10, and line L5 is a voltage/time line obtained at the above-mentioned flag signal (PFF) output terminal. As shown, an instantaneous and a long voltage drop occur at both the power supply terminal (VDD) and the reset voltage terminal (Vres) in time periods TI and T2, respectively.

Unlike the conventional abnormal voltage detecting means, the present invention can, at both the Power Failure Detector Output (PFDO) terminal and the flag signal (PFF) output terminal, detect even a very minor voltage drop present in the very short time period T1.

Numeral 1 is used to indicate a high potential and a message of abnormal condition is output as a basis to have the micro controller interrupted or reset.

From the above description, it can be seen that the apparatus of the present invention indeed has the ability to instantaneously detect abnormal voltage in a micro controller through a digital circuit of the apparatus and thereby allows the micro controller to effect an instantaneous interrupt or reset which is otherwise difficult to be done in the conventional abnormal voltage detecting means.

Although the present invention has been described with respect to a preferred embodiment thereof, it should be noted that the present invention is not limited to such embodiment and various changes can be made without departing from the scope of the present invention which is defined by the subjoined claims.

Claims

1. Apparatus for instantaneously detecting an abnormal voltage in a micro controller, comprising a detecting circuit for setting a voltage value to be detected and a latch circuit, said detecting circuit being a logic "NOT" gate which has a power supply connecting terminal connected to a reset voltage terminal of an internal circuit of said micro controller, an input terminal connected to a power supply terminal of the internal circuit of said micro controller, and an output terminal connected to a cooperating input terminal of said latch circuit; and said latch circuit having an output terminal for outputting a flag signal reflecting an abnormal voltage in said micro controller; whereby whenever there is an instantaneous change of said micro controller's voltage to a non-nominal rating, said voltage change can be instantaneously detected and be latched by a signal, causing said flag signal output from said output terminal of said latch circuit to reflect an abnormal voltage for said micro controller to effect an instantaneous interrupt or reset.

2. Apparatus for instantaneously detecting an abnormal voltage in a micro controller as claimed in claim 1, wherein said detecting circuit is a CMOS logic "NOT" gate.

3. Apparatus for instantaneously detecting an abnormal voltage in a micro controller as claimed in claim 1 or 2, wherein said latch circuit is a flip-flop.

4. Apparatus for instantaneously detecting an abnormal voltage in a micro controller as claimed in claim 1 or 2, wherein said latch circuit is a latch functionally equivalent to a flip-flop.

5. Apparatus for instantaneously detecting an abnormal voltage in a micro controller as claimed in claim 3, wherein said flip-flop has a CB terminal connected to the output terminal of said logic "NOT" gate, a D terminal and a power supply connecting terminal together connected to said reset voltage terminal of said micro controller, and a Q output terminal and an R output terminal for outputting flag signals reflecting said abnormal voltage.

6. Apparatus for instantaneously detecting an abnormal voltage in a micro controller as claimed in claim 3, wherein said detecting circuit has a detecting potential which can be set through a mask option to meet the requirements of an entire system in which said apparatus and said micro controller are incorporated.

7. Apparatus for instantaneously detecting an abnormal voltage in a micro controller, substantially as hereinbefore described with reference to and as shown in Figs. 2 and 3 of the accompanying drawings.