CN104113348B - Device and control method for the key scan under multidigit nixie tube drive environment - Google Patents

Abstract

The invention relates to a device and a control method thereof for button scanning in a multi-digit digital tube driving environment; the I/O port of the device has an output buffer, a decoding device, a comparing device, a switch and multiple built-in voltages; This control method uses the reasonably selected button scanning voltage V _S and the button scanning default voltage V _PD to scan the buttons, and the driving ability of V _PD is less than the driving ability of V _S , so that the digital tube display drive port can be reused for button scanning, and No additional I/O ports and peripheral components are needed, the number of I/O ports used for digital tube display driving and key scanning in the display driver chip and the peripheral components of the display driver chip are reduced, and the I/O of the display driver chip is improved. The utilization rate of /O resources reduces the packaging and PCB board cost of the display driver chip, improves the stability of the system, and reduces the area of the PCB board.

Description

Device and control method for button scanning in multi-digit digital tube driving environment

technical field

The invention relates to a key scanning technology, in particular to a key scanning device and control method used in a multi-digit nixie tube driving environment.

Background technique

Digital tubes can be divided into common anode digital tubes and common cathode digital tubes according to the connection mode of the light-emitting diode units. The common anode digital tube refers to the digital tube that connects the anodes of all light-emitting diodes together to form a common anode (com). When the common anode digital tube is applied, the common pole should be connected to a high level. When a certain field (seg) emits light When the cathode of the diode is low, the corresponding field is lit. The common cathode digital tube refers to the digital tube that connects the cathodes of all light-emitting diodes together to form a common cathode (com). When the common cathode digital tube is applied, the common pole should be connected to a low level. When a certain field (seg) emits light When the anode of the diode is high, the corresponding field is lit. Common nixie tubes are 8-segment nixie tubes, and each 1-bit nixie tube includes 7 fields (a, b, c, d, e, f, g) in the shape of "day" and a "decimal point" field(dp).

In the traditional technical scheme 1, the seg end of each digital tube multiplexes the I/O port of the display driver chip, and the corresponding I/O port is called the seg port; and the com ports of different digital tubes are respectively connected to the display driver chip Other I/O ports on the computer, the corresponding I/O ports are called com ports. The display driver chip drives each nixie tube in a time-division multiplexing manner, so that each nixie tube displays in turn in a cycle.

In Fig. 1, the seg ends of the digital tubes LED1 and LED2 share the I/O ports S1-S8 of the display driver chip, while the com ends are respectively connected to S9 and S10. The I/O ports S1-S8 are connected to the rows of the key array, and S9 and S10 are connected to the columns of the key array.

In Fig. 2, V _H represents the high voltage output by the I/O port, V _L represents the low voltage output by the I/O port, and Z represents the high-impedance state of the I/O port. Nixie tube display and key scanning are carried out in time-sharing. In the display time slot of the digital tube, the independent I/O port controls the com terminal of the digital tube to drive each digital tube to display in sequence. In a key scan time slot, the I/O port scans the key array row by row or column by column.

In the traditional technical scheme 1, only one com port of the display driver chip is valid in the display time slot of each nixie tube, and the other com ports are in an invalid or idle state, so as to ensure that other nixie tubes are not strobed. The traditional technical solution one is to drive the display of the digital tube only through the high voltage V _H and the low voltage V _L in the display time slot of the digital tube. Therefore, in order not to cause multiple digital tubes to display at the same time, the com port must be an independent I/O port, and the number of com ports is equal to the number of digital tubes. Therefore, driving a 1-digit 8-segment digital tube requires 1 com port and 8 seg ports, and a total of 9 I/O ports are required; driving a 2-digit 8-segment digital tube requires 2 com ports and 8 seg ports, and a total of 10 I/O ports; M com ports and N seg ports are required to drive M-bit N-segment digital tubes, and a total of M+N I/O ports are required. In the application of multi-digit digital tube display driver, this solution will occupy more I/O ports of the chip. Too many display driver ports lead to higher chip cost and packaging cost.

In 2003, Charlie Allen of Maxim proposed the Charlieplexing technology, using the state characteristics of the I/O port and the one-way conduction principle of the light-emitting diode to realize the multiplexing of the com port and the seg port in the display time slot of the digital tube, reducing the number of The digital tube displays the number of I/O ports required by the driver.

In Fig. 3, the com terminals of the digital tubes LED1~LED10 are respectively connected to the I/O ports S1~S10 of the chip. The 8 seg terminals of LED1 are connected to the I/O ports other than S1, namely S2～S9; the 8 seg terminals of LED2 are connected to the I/O ports other than S2, namely S1, S3～S9; and so on, LED10 The 8 seg ends of the S10 are connected to I/O ports other than S10, namely S1-S8.

In Figure 4, in the display time slot of the digital tube, the I/O port is no longer independently divided into com port and seg port, but the com port and seg port are combined together, and the com port is distinguished by time division multiplexing and seg ports. In terms of connection, an I/O port is not only the seg port of a digital tube, but also the com port of another digital tube.

However, when this method uses the digital tube display driver port for key scanning through time division multiplexing, it needs to occupy an additional I/O port or use peripheral components, otherwise the key scanning will affect the display of the digital tube. In this technical scheme, the I/O port serves as both the seg port of one digital tube and the com port of another digital tube, and any two I/O ports may be connected to both ends of a field. Therefore, to make all fields unlit during the key scan time slot, no voltage difference between any two I/O ports is allowed. Key scanning is realized by detecting the level change of the I/O port, so in the key scanning time slot, there must be a voltage difference between some I/O ports. If the digital tube display driver port is multiplexed as the key scanning port, some fields will be lit during the key scanning time slot, causing the digital tube display to be confused. To sum up, this technical solution cannot reuse the digital tube display driver port for key scanning without occupying additional I/O ports or using peripheral components. In the application scenarios of digital tube display driver and key scanning, especially in the case of multiple digital tubes and multiple keys, this solution will occupy more I/O ports.

Contents of the invention

The purpose of the present invention is to overcome the defects in the prior art, to provide a method that saves the occupation of the I/O resources of the display driver chip, reduces the number of pins of the display driver chip, reduces the packaging cost of the display driver chip, and reduces the number of display driver chips. The peripheral components and parts of the chip, the device and the control method used for key scanning under the drive environment of multi-bit digital tubes can improve the stability of the system.

The technical solution for realizing the object of the present invention is: the device used for key scanning under the multi-digit digital tube driving environment includes a display driver chip, and the display driver chip has a plurality of I/O ports; the I/O port has a plurality of A built-in voltage, including high voltage V _H and low voltage V _L for digital tube display driving, key scanning voltage V _S for key scanning and key scanning default voltage V _PD , and reference voltage V _K ; the key scanning The driving capability of the default voltage V _PD is less than the driving capability of the key scanning voltage V _S ; the I/O port has an output buffer, a decoding device, a comparison device, a switch S1, and a switch S2; the output buffer has enabling and Two states are not enabled.

As shown in Fig. 5, the power supply end of the output buffer is connected to the high voltage V _H and the low voltage V _L , the input end of the output buffer is connected to the signal Disp _out end, and the output end of the output buffer is connected to the I/O port; the translation The input end of code device is respectively connected with nixie tube display enable signal EN _Disp end and button scanning enable signal EN _Key end, and the output end of decoding device is respectively connected the enable end of output buffer and the controlled end of switch S1; The comparison device has a reference voltage V _K , the input terminal of the comparison device is connected to the common end of switches S1 and S2, and the output terminal of the comparison device is connected to the signal Key _in end; the selection terminal of the switch S1 is according to the state of its control signal and I/ The O ports are connected or disconnected; the controlled end of the switch S2 is connected to the control signal Key _out , and the selection end of the switch S2 is connected to the key scan voltage V _S or the key scan default voltage V _PD according to the state of the control signal Key _out .

The decoding device controls the enable state of the output buffer and the on-off state of the switch S1, and the decoding device can be realized by different logic circuits. The decoding device may be composed of an AND gate and a NOT gate; the input terminals of the AND gate are respectively connected to the nixie tube display enable signal EN _Disp end and the output terminal of the NOT gate, and the output terminals of the AND gate are connected to the output buffer The enable end of the NOT gate; the input end of the NOT gate is connected to the EN _Key end of the key scanning enable signal and the controlled end of the switch S1.

The comparison device compares the input signal of the I/O port with the magnitude of the reference voltage V _K , and its output is used to determine the logic level of the input signal of the I/O port. The comparison device may be a comparator, and the reference voltage V _K is an external reference voltage connected to an input terminal of the comparator. The comparison device may be a buffer, and the reference voltage V _K is a built-in flip voltage of the buffer.

The reference voltage V _K , key scan voltage V _S , and key scan default voltage V _PD satisfy the inequality V _PD <V _K <V _S or V _S <V _K <V _PD .

The driving capability of the default key scanning voltage V _PD is weak, and when the I/O port set to the key scanning default voltage V _PD is connected to the key scanning voltage V _S , the voltage state of the I/O port changes. The key scanning default voltage V _PD can be provided by a voltage series resistor R; one end of the resistor R is connected to the voltage, and the other end is connected to the selection end of the switch S2.

The control method for button scanning in a multi-digit digital tube driving environment is suitable for high-level or low-level active button scanning; during button scanning, all I/O ports are set to the default voltage V _PD of button scanning, and the scanning Output button scan voltage V _S to one end of the button when the button is pressed; detect the voltage of the other end of the corresponding button; judge whether the button is pressed by comparing the voltage with the reference voltage V _K ; the button scan voltage V _S and the button scan default The voltage V _PD is different from the high voltage V _H and the low voltage V _L that drive the digital tube display. There is a voltage difference between the key scan voltage V _S and the key scan default voltage V _PD that cannot drive the digital tube to light up or cannot The maximum current I that can drive the digital tube to light up.

There is a voltage difference between the button scanning voltage V _S and the button scanning default voltage V _PD described in the above technical solution, which cannot drive the digital tube to light up, and the voltage difference satisfies the following inequality:

|V _S -V _PD |< the turn-on voltage V _LED of the field of the nixie tube.

There is a maximum current I that cannot drive the digital tube to light between the key scanning voltage V _S and the key scanning default voltage V _PD described in the above technical solution, and the maximum current I satisfies the following inequality:

The maximum current I between V _S and V _PD < the conduction current I _LED of the field of the digital tube.

After adopting the technical scheme, the present invention has the following positive effects:

(1) The present invention can apply Charlieplexing technology to reduce the number of digital tube display drive ports, and can reuse the digital tube display drive ports for key scanning, and does not require additional I/O ports and peripheral components, greatly reducing The number of I/O ports used for digital tube display driving and button scanning in the display driver chip improves the utilization of the I/O resources of the display driver chip, reduces the packaging cost of the display driver chip, and reduces the peripheral components of the display driver chip , Improve the stability of the system, reduce the area of the PCB board, and reduce the cost of the PCB board.

(2) The present invention only needs max(M, N+1) I/O ports when driving M-bit N-segment digital tubes, and these max(M, N+1) I/O ports can all be time-division multiplexed The method used is used for key scanning. Wherein, the value of max(M,N+1) is a larger positive integer among M and N+1.

(3) The present invention prevents the display drive of the digital tube from interacting with the key scanning. In particular, when the I/O port scans the key, it will not affect the display effect of the digital tube, making the display of the digital tube more stable.

Description of drawings

In order to make the content of the present invention easier to understand clearly, the present invention will be described in further detail below according to specific embodiments in conjunction with the accompanying drawings, wherein

Fig. 1 is the structural representation of traditional technical scheme one;

Fig. 2 is the working principle diagram of traditional technical scheme one;

Fig. 3 is the structural representation of traditional technical scheme two;

Fig. 4 is the working principle figure of traditional technical scheme two;

5 is a functional structural diagram of the I/O port of the display driver chip of the present invention;

6 is a circuit diagram of an I/O port of a display driver chip according to Embodiment 1 of the present invention;

7 is a circuit diagram of an I/O port of a display driver chip according to Embodiment 2 of the present invention;

Fig. 8 is a diagram showing the circuit connection relationship between the display driver chip and the peripheral digital tubes and keys of the present invention;

FIG. 9 is a working principle diagram of the display driver chip of the present invention.

detailed description

(Example 1)

See Fig. 5, Fig. 6, Fig. 8 and Fig. 9, this embodiment is a typical application case of digital tube display and key scanning.

In this embodiment, a display driver chip uses 10 I/O ports to drive the display of 10-bit common-cathode 8-segment digital tubes, and scans 25 keys (more or fewer keys can be realized by different connection methods).

See Fig. 6, the device that is used for the button scanning under the driving environment of multi-bit nixie tube, comprises display driver chip, and display driver chip has a plurality of I/O ports; I/O port has output buffer 1, decoding device 2, Comparing device 3, switch S1, switch S2 and multiple built-in voltages; the output buffer has two states of enable and disable; built-in voltages include high voltage V _H , low voltage V _L , reference voltage V _K , and key scanning voltage V _S , key scan default voltage V _PD . The power supply end of the output buffer 1 is connected to the high voltage V _H and the low voltage V _L , the input end of the output buffer 1 is connected to the signal Disp _out end, and the output end of the output buffer 1 is connected to the I/O port; the decoding The input terminals of the device 2 are respectively connected to the digital tube display enabling signal EN _Disp terminal and the button scanning enabling signal EN _Key terminal, and the output terminals of the decoding device 2 are respectively connected to the enabling terminal of the output buffer 1 and the controlled terminal of the switch S1 The comparison device 3 has a reference voltage V _K , the input terminal of the comparison device 3 is connected to the common end of switches S1 and S2, and the output terminal of the comparison device 3 is connected to the signal Key _in end; the selection terminal of the switch S1 is according to its control signal The state of the switch S2 is connected or disconnected with the I/O port; the controlled end of the switch S2 is connected to the control signal Key _out end, and the selection end of the switch S2 is connected to the key scanning voltage V _S or key scanning default according to the state of the control signal Key _out end. voltage V _PD . The reference voltage V _K , the key scan voltage V _S , and the key scan default voltage V _PD satisfy the inequality V _PD <V _K <V _S or V _S <V _K <V _PD .

The decoding device 2 can be realized by different logic circuits. In this embodiment, the decoding device 2 is composed of an AND gate 2.1 and a NOT gate 2.2; the input terminals of the AND gate 2.1 are respectively connected to the nixie tube display enable signal EN _Disp end and the output terminal of the NOT gate 2.2, and the output of the AND gate 2.1 The terminal is connected to the enable terminal of the output buffer 1; the input terminal of the NOT gate 2.2 is connected to the EN _Key terminal of the button scanning enable signal and the controlled terminal of the switch S1.

The comparison device 3 may have various circuit implementation forms. In this embodiment, the comparison device 3 is a comparator 3.1, the non-inverting input terminal of the comparator 3.1 is connected to the common terminal of the switches S1 and S2, and the output terminal of the comparator 3.1 is connected to the signal Key _in terminal; the reference voltage V _K is the comparator 3.1 The external reference voltage connected to the negative input terminal, refer to Figure 6.

The key scan default voltage V _PD can be realized in various ways. In this embodiment, the key scanning default voltage V _PD is provided by a voltage series resistor R; one end of the resistor R is connected to the voltage, and the other end is connected to the selection end of the switch S2.

As shown in Figure 6, when the I/O port is used to drive the digital tube, the display driver chip sets the EN _Key to logic 0, and the switch S1 of the input channel in the I/O port is turned off. When EN _Disp is logic 1, the output buffer 1 is enabled and the Disp _out signal is output, and the Disp _out signal is output after being buffered by the output buffer 1, and the I/O port outputs a high voltage V _H or a low voltage accordingly V _L . When setting EN _Disp to logic 0, the output buffer 1 is disabled, the drive transistors in the output buffer 1 are all cut off, and the I/O port is correspondingly in the high-impedance state Z. When the I/O port is used for scanning keys, the display driver chip sets the EN _Key as logic 1, the switch S1 of the input channel in the I/O port is closed, and the output buffer 1 is disabled. When Key _out is logic 1, switch S2 is connected to V _S , and the I/O port outputs V _S accordingly. When Key _out is logic 0, the switch S2 is connected to the resistor R, and the I/O port outputs V _PD accordingly. V _K is the input reference voltage of the comparator 3.1 in the input channel. The output Key _in of the comparator 3.1 is used to determine the logic level of the input signal (logic 1 or logic 0). The comparator 3.1 here can also use the built-in flip voltage A suitable buffer 3.2 is implemented, see FIG. 7 . In this embodiment, V _S and V _PD satisfy the inequalities V _PD <V _K <V _S and V _K −V _PD <V _S −V _PD <V _LED .

As shown in Figure 8, the com terminals of the digital tubes LED1-LED10 are respectively connected to the I/O ports S1-S10 of the display driver chip, and the seg terminals of the digital tubes are connected to other I/O ports. That is: the com terminal of the digital tube LED1 is connected to the I/O port S1 of the display driver chip, and its seg terminal is connected to the I/O ports S2~S9; the com terminal of the digital tube LED2 is connected to the I/O port of the display driver chip S2, its seg terminal is connected to the I/O port S1, S3 ~ S9; and so on, the com terminal of the digital tube LED10 is connected to the I/O port S10 of the display driver chip, and its seg terminal is connected to the I/O port S1 ~S8. The I/O ports S1-S5 of the display driver chip are respectively connected to each column of the key array, and S6-S10 are respectively connected to each row of the key array. When the com terminal of the digital tube is a low voltage V _L , the digital tube is selected; when the seg terminal of the selected digital tube is a high voltage V _H , the corresponding field is lit.

The key scan port is divided into a key scan input port and a key scan output port. Referring to FIG. 8, I/O ports S1-S5 are used as key scanning input ports, and I/O ports S6-S10 are used as key scanning output ports. During key scanning, all I/O ports are set to the default voltage V _PD for key scanning; when scanning keys, I/O ports S6-S10 output V _S successively, and the display driver chip scans the key array line by line. For example, when the I/O port S6 outputs V _S , the display driver chip detects the buttons SW1~SW5 in the first row. If the button SW1 is pressed, the I/O port S1 is set to V _S by S6, and the I/O Port S1 is logic 1.

The display driver chip works periodically, drives the digital tube to display and scans the keys in each cycle. One cycle is divided into digital tube display time slot and button scanning time slot. In the display time slot of the digital tube, each digital tube displays its content in turn, so the display time slot of the digital tube is divided into multiple small time slots. In the key scanning time slot, the display driver chip scans the key progressively.

See Fig. 9, in this embodiment, the digital tube display time slot is divided into 10 small display time slots, and the 10 digital tubes LED1-LED10 display their contents in their respective display time slots. During display time slot 1, the I/O port S1 of the display driver chip outputs a low voltage V _L to gate LED1, and the I/O ports S2-S9 output a high voltage V _H or are in a high-impedance state Z according to the display content of LED1 , the I/O port S10 that has nothing to do with LED1 maintains a high-impedance state Z. During the display time slot 2, the I/O port S2 of the display driver chip outputs a low voltage V _L to gate the digital tube LED2, and the I/O ports S1, S3~S9 output a high voltage V _H according to the display content of LED2 or at High resistance state Z, the I/O port S10 which has nothing to do with the digital tube LED2 maintains high resistance state Z. By analogy, during the display time slot 10, the I/O port S10 of the display driver chip outputs a low voltage V _L to gate the digital tube LED10, and the I/O ports S1-S8 output a high voltage V L according to the display content of the digital tube LED10 _H or in a high-impedance state Z, and the I/O port S9 that has nothing to do with the digital tube LED10 maintains a high-impedance state Z. So far, the nixie tube shows that the time slot is completed.

After the time slot displayed on the nixie tube, it is the key scanning time slot. In this time slot, the key scan output ports S6-S10 output V _PD when they are invalid. When the voltage at both ends of the field in the digital tube is V _PD , the voltage difference between the two ends of the field is 0, so these fields are not bright. In this time slot, the key scanning output ports S6-S10 output V _S when they are valid. When the key scanning output port S6 outputs V _S , the display driver chip scans the keys SW1-SW5 in the first row. Assuming that SW1 is not pressed, the voltage difference between S6 and S1 is V _S -V _PD , that is, the forward voltage across the e-field of the digital tube LED1 is V _S -V _PD , since V _S -V _PD <V _LED , so the field is not lit at this time. There are many more fields in this case, but none of them are lit because their forward voltage drop is low enough to turn it on. Assuming that the button SW1 is pressed, the port S1 is set to V _S by S6, as before, this will not cause abnormal display of the digital tube. The key scan output ports S6-S10 output V _S sequentially, and the display driver chip detects the key scan input ports S1-S5 of each row. After the display driver chip detects the fifth row of keys, the key scanning time slot ends. In a word, during the entire key scanning time slot, the voltage at each I/O port only changes between V _S and V _PD , so the key scanning will not affect the display of the digital tube.

Compared with the traditional technical solutions, it can be seen that the control method of the present invention does not use high voltage V _H and low voltage V _L to scan keys, but selects reasonable key scanning voltage V _S and key scanning default voltage V _PD . Proper selection of key scanning voltage V _S and key scanning default voltage V _PD ensures the independence of digital tube display driver and key scanning when I/O ports are multiplexed, and ensures the correctness of digital tube display and key scanning.

Under the control method of the present invention, the display driver chip can drive 10 digital tubes and can scan 25 keys. It can be seen that the control method of the present invention enables the display driver chip to drive more digital tubes and scan keys. In other words, by adopting the control method of the present invention, the display driver chip needs fewer I/O ports when driving multi-digit digital tubes and scanning keys.

The control method of the invention is suitable for display driving of common anode or common cathode digital tubes, and suitable for key scanning with high level or low level effective.

To sum up, by adopting the control method of the present invention, the display driver chip can realize the multiplexing of the display drive port and the key scanning port of the digital tube while multiplexing the com terminal and the seg terminal of the digital tube. The control method of the present invention is especially suitable for the application occasion of driving multiple digital tubes to display joint scanning keys. The control method of the present invention can greatly save the occupation of the I/O resources of the display driver chip, reduce the number of pins of the display driver chip, reduce the packaging cost of the display driver chip, reduce the peripheral components of the display driver chip, and improve the system performance. The stability of the PCB board is reduced, and the cost of the PCB board is reduced.

(Example 2)

Wherein, the comparison device 3 can also be a buffer 3.2, the input end of the buffer 3.2 is connected to the common end of the switches S1 and S2, and the output end is connected to the signal Key _in end; the reference voltage V _K is the built-in flip voltage of the buffer 3.2, refer to Fig. 7.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. The device used for key scanning under the driving environment of multi-digit digital tubes, comprising a display driver chip, is characterized in that: the display driver chip has a plurality of I/O ports; the I/O port has a plurality of built-in voltages ; The built-in voltage includes high voltage VH and low voltage VL for nixie tube display drive, key scanning voltage VS for key scanning and key scanning default voltage VPD, and reference voltage VK; described key scanning default voltage VPD The drive capability is less than the drive capability of the button scanning voltage VS; the I/O port has an output buffer (1), a decoding device (2), a comparison device (3), a switch S1, a switch S2; the output buffer ( 1) It has two states of enable and disable, the power supply terminal of the output buffer (1) is connected to the high voltage VH and the low voltage VL, the input terminal of the output buffer (1) is connected to the signal Dispout end, and the signal The display signal is connected to the Dispout end, and the output end of the output buffer (1) is connected to the I/O port; the output end of the decoding device (2) is respectively connected to the enable end of the output buffer (1) and the controlled end of the switch S1 , the decoding device controls the enable state of the output buffer and the on-off state of the switch S1; the comparison device (3) has a reference voltage VK, and the input terminal of the comparison device (3) is connected to the common end of the switches S1 and S2 , the output terminal of the comparison device (3) is connected to the signal Keyin end, and the comparison device compares the voltage of the I/O port input signal with the size of the reference voltage VK, and its output is used to determine the logic level of the I/O port input signal; The selection terminal of the switch S1 is connected or disconnected with the I/O port according to the state of the control signal; the controlled terminal of the switch S2 is connected to the control signal Keyout terminal, and the selection terminal of the switch S2 is connected according to the state of the control signal Keyout terminal Key scan voltage VS or key scan default voltage VPD. 2. the device that is used for the button scanning under the multi-digit nixie tube driving environment according to claim 1, is characterized in that: the input end of described decoding device (2) is respectively connected nixie tube display enabling signal ENDisp end and Button scanning enable signal ENKey terminal. 3. the device for the button scanning under the multi-digit nixie tube drive environment according to claim 1, is characterized in that: described decoding device (2) is made up of AND gate (2.1) and NOT gate (2.2); The input end of described AND gate (2.1) is respectively connected the output end of nixie tube display enabling signal ENDisp end and NOT gate (2.2), and the output end of AND gate (2.1) is connected the enabling end of output buffer (1); The input end of the NOT gate (2.2) is connected to the ENKey end of the key scanning enable signal and the controlled end of the switch S1. 4. The device for key scanning under multi-digit nixie tube drive environment according to claim 1, characterized in that: said comparison device (3) is a comparator (3.1), and said reference voltage VK is a comparator The input of (3.1) is connected to the external reference voltage. 5. The device for scanning keys under a multi-digit nixie tube driving environment according to claim 1, characterized in that: the comparison device (3) is a buffer (3.2), and the reference voltage VK is a buffer (3.2) built-in flip voltage. 6. The device for key scanning in a multi-digit nixie tube driving environment according to claim 1, characterized in that: said reference voltage VK, key scanning voltage VS, and key scanning default voltage VPD satisfy the inequality VPD<VK< VS or VS<VK<VPD. 7. The device for button scanning in a multi-digit nixie tube driving environment according to claim 1, characterized in that: said button scanning default voltage VPD is provided by a voltage source series resistor R; One end is connected to the voltage source, and the other end is connected to the selection end of the switch S2. 8. The control method for the button scanning under the driving environment of multi-bit nixie tubes is characterized in that: the control method is suitable for high-level or low-level effective button scanning; during the button scanning, all I/O ports Set as the default voltage VPD for button scanning, output button scanning voltage VS to one end of the button when scanning the button; detect the voltage at the other end of the corresponding button; judge whether the button is pressed by comparing the voltage at the other end of the button with the reference voltage VK ; The button scan voltage VS and the button scan default voltage VPD are different from the high voltage VH and the low voltage VL displayed by the drive digital tube, and there is a point that cannot drive the digital tube between the button scan voltage VS and the button scan default voltage VPD Bright voltage difference, the voltage difference satisfies the following inequality: |VS-VPD|<the conduction voltage VLED of the field of the digital tube, or there is a point that cannot drive the digital tube between the key scan voltage VS and the key scan default voltage VPD Bright maximum current I, and the maximum current I satisfies the following inequality: the maximum current I between VS and VPD<the conduction current ILED of the field of the digital tube.