CN114371774B - A Protection Circuit of RS232 Interface with Isolation Function - Google Patents

The invention discloses an RS232 interface protection circuit with an isolation function, which comprises a computer side TXD circuit, a chip side RXD circuit, a computer side RXD circuit and a chip side TXD circuit, wherein the computer side TXD circuit is connected with the chip side RXD circuit through a first bus; and the circuits are mutually combined, so that the isolation conversion of the TTL level and the RS232 level is realized, and the problem of interface damage is solved.

一种具有隔离功能的RS232接口保护电路A Protection Circuit of RS232 Interface with Isolation Function

技术领域technical field

本发明涉及一种保护电路，具体涉及一种具有隔离功能的RS232接口保护电路。The invention relates to a protection circuit, in particular to an RS232 interface protection circuit with an isolation function.

背景技术Background technique

当前，很多工业控制机的电路系统常采用RS232接口和计算机通信。由于工业控制机的电路系统的核心控制芯片一般采用TTL数字电平标准，而标准计算机的RS232接口高低电平采用+3—+15V和-3—-15V，其间的电平转换普遍采用芯片MAX232C或类似具有电平转换功能的芯片完成。在工业实际使用中，电平转换芯片经常损坏，修复时需要更换芯片，造成很大的人力物力浪费。为了解决这个问题，本发明专利提出一种接口设计新方案，能有效保护接口电路不受损坏。At present, the circuit systems of many industrial control machines often use RS232 interface to communicate with computers. Because the core control chip of the circuit system of the industrial control machine generally adopts the TTL digital level standard, while the high and low level of the RS232 interface of the standard computer adopts +3—+15V and -3——15V, and the level conversion generally adopts the chip MAX232C Or a similar chip with level shifting function is done. In actual industrial use, the level conversion chip is often damaged, and the chip needs to be replaced when it is repaired, resulting in a great waste of manpower and material resources. In order to solve this problem, the patent of the present invention proposes a new interface design scheme, which can effectively protect the interface circuit from damage.

发明内容Contents of the invention

为了克服现有技术中的缺陷，本发明提供一种具有隔离功能的RS232接口保护电路。In order to overcome the defects in the prior art, the present invention provides an RS232 interface protection circuit with isolation function.

本发明通过下述方式实现：The present invention is realized in the following manner:

方案一：一种具有隔离功能的RS232接口保护电路，包括计算机侧TXD电路和芯片侧RXD电路；Solution 1: An RS232 interface protection circuit with isolation function, including a computer-side TXD circuit and a chip-side RXD circuit;

计算机侧TXD电路包含：计算机TXD发送端口、第四二极管D4、第七电阻R7和第三电流变压器T3；计算机TXD发送端口和计算机信号GND之间依次串联有第三电流变压器T3的高压侧线圈、第四二极管D4和第七电阻R7，第四二极管D4的阳极与计算机信号GND连接；计算机TXD发送端口与第三电流变压器T3的高压侧线圈的负极端连接；The TXD circuit on the computer side includes: the computer TXD sending port, the fourth diode D4, the seventh resistor R7 and the third current transformer T3; the high voltage side of the third current transformer T3 is serially connected in series between the computer TXD sending port and the computer signal GND The coil, the fourth diode D4 and the seventh resistor R7, the anode of the fourth diode D4 is connected to the computer signal GND; the computer TXD sending port is connected to the negative terminal of the high-voltage side coil of the third current transformer T3;

芯片侧RXD电路包含：芯片RXD接收端口、电压源VCC、第八电阻R8、第九电阻R9、第三三极管Q3；芯片RXD接收端口连接第三三极管Q3的集电极，第三三极管Q3的集电极和电压源VCC之间串联有第八电阻R8，第三三极管Q3的发射极与芯片接地端GND连接，第三三极管Q3的基极与芯片接地端GND之间依次第九电阻R9和第三电流变压器T3的低压侧线圈，第三电流变压器T3的低压侧线圈的负极端与芯片接地端GND连接。The RXD circuit on the chip side includes: the chip RXD receiving port, the voltage source VCC, the eighth resistor R8, the ninth resistor R9, and the third transistor Q3; the chip RXD receiving port is connected to the collector of the third transistor Q3, and the third and third An eighth resistor R8 is connected in series between the collector of the transistor Q3 and the voltage source VCC, the emitter of the third transistor Q3 is connected to the chip ground terminal GND, and the base of the third transistor Q3 is connected to the chip ground terminal GND. Between the ninth resistor R9 and the low-voltage side coil of the third current transformer T3 in turn, the negative end of the low-voltage side coil of the third current transformer T3 is connected to the chip ground terminal GND.

方案二：一种具有隔离功能的RS232接口保护电路，包括计算机侧TXD电路和芯片侧RXD电路；Scheme 2: An RS232 interface protection circuit with isolation function, including a computer-side TXD circuit and a chip-side RXD circuit;

计算机侧TXD电路包含：计算机TXD发送端口、第一二极管D1、第一电阻R1和发光二极管；计算机TXD发送端口和发光二极管的阴极连接，发光二极管的阳极依次与第一电阻R1、第一二极管的阴极连接，第一二极管的阳极与计算机信号GND连接；The TXD circuit on the computer side includes: computer TXD sending port, first diode D1, first resistor R1 and light-emitting diode; the computer TXD sending port is connected to the cathode of the light-emitting diode, and the anode of the light-emitting diode is sequentially connected to the first resistor R1, the first The cathode of the diode is connected, and the anode of the first diode is connected with the computer signal GND;

芯片侧RXD电路包含：芯片RXD接收端口、电压源VCC、第二电阻R2、光敏三极管；芯片RXD输入端口与光敏三极管的集电极连接，光敏三极管的集电极与电压源VCC之间串联第二电阻R2，光敏三极管的发射极与芯片接地端GND连接；发光二极管与光敏三极管组成光耦合器OE1。The RXD circuit on the chip side includes: the chip RXD receiving port, the voltage source VCC, the second resistor R2, and the phototransistor; the chip RXD input port is connected to the collector of the phototransistor, and the second resistor is connected in series between the collector of the phototransistor and the voltage source VCC R2, the emitter of the phototransistor is connected to the ground terminal GND of the chip; the light emitting diode and the phototransistor form an optical coupler OE1.

方案三：一种具有隔离功能的RS232接口保护电路，包括计算机侧RXD电路和芯片侧TXD电路；Scheme 3: An RS232 interface protection circuit with isolation function, including a computer-side RXD circuit and a chip-side TXD circuit;

芯片侧TXD电路包含：芯片TXD发送端口、第一三极管Q1、第二三极管Q2、第一电流变压器T1、第二电流变压器T2、第四电阻R4、第六电阻R6、电压源VCC；第一三极管Q1为PN P晶体管，第二三极管Q2为NPN晶体管；芯片TXD发送端口分别连接第一三极管Q1的基极和第二三极管Q2的基极；电源源VCC与第一三极管Q1的发射极之间依次串联第四电阻和第一电流变压器的低压侧，第一三极管Q1的集电极与接地端GND连接；电源源VCC与第二三极管Q2的集电极依次串联第六电阻、第二电流变压器的低压侧，第二三极管Q2的发射极与芯片接地端GND连接；The TXD circuit on the chip side includes: chip TXD sending port, first transistor Q1, second transistor Q2, first current transformer T1, second current transformer T2, fourth resistor R4, sixth resistor R6, voltage source VCC ; The first transistor Q1 is a PNP transistor, and the second transistor Q2 is an NPN transistor; the TXD sending port of the chip is respectively connected to the base of the first transistor Q1 and the base of the second transistor Q2; the power source The fourth resistor and the low-voltage side of the first current transformer are connected in series between VCC and the emitter of the first triode Q1, the collector of the first triode Q1 is connected to the ground terminal GND; the power source VCC is connected to the second triode The collector of the transistor Q2 is connected in series with the sixth resistor and the low-voltage side of the second current transformer, and the emitter of the second triode Q2 is connected to the chip ground terminal GND;

计算机侧RXD电路包含：计算机RXD接收端口、第三电阻R3、第五电阻R5、第二二极管D2、第三二极管D3；计算机RXD接收端口分别连接第一电流变压器T1的高压侧线圈的负极端和第二电流变压器T2的高压侧线圈的正极端；第一电流变压器T1的高压侧线圈的正极端与计算机信号GND之间依次串联第三电阻R3和第二二极管D2，第二二极管D2的阳极与计算机信号GND连接；第二电流变压器T2的高压侧线圈的负极端与计算机信号GND之间依次串联第五电阻R5和第三二极管D3，第三二极管D3的阴极与计算机信号GND连接。The RXD circuit on the computer side includes: the computer RXD receiving port, the third resistor R3, the fifth resistor R5, the second diode D2, and the third diode D3; the computer RXD receiving port is respectively connected to the high-voltage side coil of the first current transformer T1 The negative end of the current transformer T2 and the positive end of the high-voltage side coil of the second current transformer T2; the third resistor R3 and the second diode D2 are connected in series in series between the positive end of the high-voltage side coil of the first current transformer T1 and the computer signal GND, and the first The anode of the second diode D2 is connected to the computer signal GND; the fifth resistor R5 and the third diode D3 are connected in series in sequence between the negative end of the high-voltage side coil of the second current transformer T2 and the computer signal GND, and the third diode The cathode of D3 is connected to the computer signal GND.

方案四：由方案一和方案三合并而成。Scheme 4: Combination of Scheme 1 and Scheme 3.

方案五：由方案二和方案三合并而成。Scheme 5: Combination of Scheme 2 and Scheme 3.

与现有技术相比，本发明的有益效果为：本发明提出一种接口保护电路，将TTL电平和RS232电平转换隔离设计，互不影响，通过本发明可以彻底解决接口的损坏问题。Compared with the prior art, the beneficial effects of the present invention are: the present invention proposes an interface protection circuit, and the TTL level and RS232 level conversion are isolated and designed without mutual influence, and the damage problem of the interface can be completely solved by the present invention.

附图说明Description of drawings

下面结合附图和具体实施例对本发明做进一步详细说明。The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

图1为常见的RS232电平转化电路图；Figure 1 is a common RS232 level conversion circuit diagram;

图2为本发明的一种计算机侧TXD电路和芯片侧RXD电路连接图；Fig. 2 is a connection diagram of a computer side TXD circuit and a chip side RXD circuit of the present invention;

图3为本发明的另一种计算机侧TXD电路和芯片侧RXD电路连接图；Fig. 3 is another kind of computer side TXD circuit and chip side RXD circuit connection diagram of the present invention;

图4为本发明的计算机侧RXD电路和芯片侧TXD电路电路连接图。Fig. 4 is a circuit connection diagram of the computer-side RXD circuit and the chip-side TXD circuit of the present invention.

具体实施方式Detailed ways

下面将结合实施例对本发明的实施方案进行详细描述，但是本领域的技术人员将会理解，下列实施例仅用于说明本发明，而不应视为限制本发明的范围。Embodiments of the present invention will be described in detail below in conjunction with examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention.

如图1所示，常见的RS232电平转换电路中，PC-RX、PC-TX和PC GND来自计算机，是标准的RS232电平，PC-RX、PC-TX的电平是相对于PC GND测得的。TXD和RXD来自控制芯片，是TTL电平，TXD和RXD的电平是相对于GND测得的。此电路正常工作的前提是PC GND和GND可靠连接。否则，PC GND和GND电平不一致，PC GND的电位可能远高于GND，造成PC-RX、PC-TX电平远高于电平转换芯片要求的安全电平，使电平转换芯片损坏。As shown in Figure 1, in the common RS232 level conversion circuit, PC-RX, PC-TX and PC GND come from the computer and are standard RS232 levels, and the levels of PC-RX and PC-TX are relative to PC GND test the result. TXD and RXD come from the control chip and are TTL levels, and the levels of TXD and RXD are measured relative to GND. The prerequisite for this circuit to work properly is that the PC GND and GND are connected reliably. Otherwise, the levels of PC GND and GND are inconsistent, and the potential of PC GND may be much higher than GND, causing the levels of PC-RX and PC-TX to be much higher than the safe level required by the level shifting chip, causing damage to the level shifting chip.

在实际使用中，由于使用中的各种偶然因素，使得PC GND和GND经常不能可靠连接。譬如：接头变形，带电插拔、接头连接松动等因素都可以造成PC GND和GND不能可靠连接。当计算机没有良好接地时，PC GND带电是常见的现象，譬如：经常会碰到这种情况，当计算机机壳接触人体时有触电的感觉，就表明计算机外壳带电，而PC GND和计算机的外壳是相连的，所以PC GND也会带电。计算机外壳带电在计算机设备老化和电网连接不良等环境中经常发生，而在使用RS232接口时PC GND和GND连接不可靠也经常发生，所以经常出现电平转换芯片损坏。修复损坏需要更换芯片，造成很大的人力物力浪费。In actual use, due to various accidental factors in use, the PC GND and GND are often not reliably connected. For example: connector deformation, live plugging, connector loosening and other factors can cause PC GND and GND not to be reliably connected. When the computer is not well grounded, it is a common phenomenon that the PC GND is charged. is connected, so PC GND is also live. The electrification of the computer shell often occurs in the environment of aging computer equipment and poor grid connection, and the unreliable connection between PC GND and GND also often occurs when using the RS232 interface, so the level conversion chip is often damaged. Repairing the damage requires replacing the chip, resulting in a great waste of manpower and material resources.

本发明具有隔离功能的RS232接口保护电路，将TTL电平和RS232电平转换隔离设计，并且计算机信号GND和芯片接地端GND也相互隔离，互不影响，可以彻底解决接口的损坏问题，具体技术方案为实施例1、实施例2、实施例3。The RS232 interface protection circuit with isolation function of the present invention is designed to isolate TTL level and RS232 level conversion, and the computer signal GND and the chip ground terminal GND are also isolated from each other without affecting each other, which can completely solve the problem of interface damage. The specific technical solution Be embodiment 1, embodiment 2, embodiment 3.

实施例1Example 1

如图2所示，一种具有隔离功能的RS232接口保护电路，包括计算机侧TXD电路和芯片侧RXD电路；As shown in Figure 2, an RS232 interface protection circuit with isolation function includes a computer-side TXD circuit and a chip-side RXD circuit;

计算机侧TXD电路包含：计算机TXD发送端口、第四二极管D4、第七电阻R7和第三电流变压器T3；计算机TXD发送端口和计算机信号GND之间依次串联有第三电流变压器T3的高压侧线圈、第四二极管D4和第七电阻R7，第四二极管D4的阳极与计算机信号GND连接；计算机TXD发送端口与第三电流变压器T3的高压侧线圈的负极端连接。The TXD circuit on the computer side includes: the computer TXD sending port, the fourth diode D4, the seventh resistor R7 and the third current transformer T3; the high voltage side of the third current transformer T3 is serially connected in series between the computer TXD sending port and the computer signal GND The coil, the fourth diode D4 and the seventh resistor R7, the anode of the fourth diode D4 is connected to the computer signal GND; the computer TXD sending port is connected to the negative terminal of the high voltage side coil of the third current transformer T3.

芯片侧RXD电路包含：芯片RXD接收端口、电压源VCC、第八电阻R8、第九电阻R9、第三三极管Q3；芯片RXD接收端口连接第三三极管Q3的集电极，第三三极管Q3的集电极和电压源VCC之间串联有第八电阻R8，第三三极管Q3的发射极与芯片接地端GND连接，第三三极管Q3的基极与芯片接地端GND之间依次第九电阻R9和第三电流变压器T3的低压侧线圈，第三电流变压器T3的低压侧线圈的负极端与芯片接地端GND连接。The RXD circuit on the chip side includes: the chip RXD receiving port, the voltage source VCC, the eighth resistor R8, the ninth resistor R9, and the third transistor Q3; the chip RXD receiving port is connected to the collector of the third transistor Q3, and the third and third An eighth resistor R8 is connected in series between the collector of the transistor Q3 and the voltage source VCC, the emitter of the third transistor Q3 is connected to the chip ground terminal GND, and the base of the third transistor Q3 is connected to the chip ground terminal GND. Between the ninth resistor R9 and the low-voltage side coil of the third current transformer T3 in turn, the negative end of the low-voltage side coil of the third current transformer T3 is connected to the chip ground terminal GND.

其中，电压源VCC为3.3V，第三电流变压器T3的电压转换比为3:1，其高压侧线圈和低压侧线圈绕向一致。Wherein, the voltage source VCC is 3.3V, the voltage conversion ratio of the third current transformer T3 is 3:1, and the winding directions of the high-voltage side coil and the low-voltage side coil are consistent.

计算机通过计算机TXD发送端口发送信号，芯片通过芯片RXD接收端口接收信号。当计算机TXD发送端口发送的是高电平+12V的信号时，第四二极管D4截止，第三电流变压器T3中无电流，第三三极管Q3不导通，芯片RXD接收端口接收到的电压源VCC供电的高电平3.3V。当计算机TXD发送端口发送的是低电平-12V时，第四二极管D4导通，第三电流变压器T3中有电流，第三三极管Q3导通，芯片RXD接收端口接收到的为低电平，这样就实现了+12V到3.3V和-12V到TTL低电平的转换。The computer sends signals through the computer TXD sending port, and the chip receives signals through the chip RXD receiving port. When the computer TXD sending port sends a high-level +12V signal, the fourth diode D4 is cut off, the third current transformer T3 has no current, the third transistor Q3 is not conducting, and the chip RXD receiving port receives The voltage source VCC supplies the high level 3.3V. When the TXD sending port of the computer sends a low level -12V, the fourth diode D4 is turned on, the third current transformer T3 has current, the third transistor Q3 is turned on, and the RXD receiving port of the chip receives Low level, thus realizing the conversion from +12V to 3.3V and -12V to TTL low level.

实施例2Example 2

如图3所示，一种具有隔离功能的RS232接口保护电路，包括计算机侧TXD电路和芯片侧RXD电路；As shown in Figure 3, a RS232 interface protection circuit with isolation function, including computer side TXD circuit and chip side RXD circuit;

计算机侧TXD电路包含：计算机TXD发送端口、第一二极管D1、第一电阻R1和发光二极管；计算机TXD发送端口和发光二极管的阴极连接，发光二极管的阳极依次与第一电阻R1、第一二极管的阴极连接，第一二极管的阳极与计算机信号GND连接。The TXD circuit on the computer side includes: computer TXD sending port, first diode D1, first resistor R1 and light-emitting diode; the computer TXD sending port is connected to the cathode of the light-emitting diode, and the anode of the light-emitting diode is sequentially connected to the first resistor R1, the first The cathode of the diode is connected, and the anode of the first diode is connected with the computer signal GND.

芯片侧RXD电路包含：芯片RXD接收端口、电压源VCC、第二电阻R2、光敏三极管；芯片RXD输入端口与光敏三极管的集电极连接，光敏三极管的集电极与电压源VCC之间串联第二电阻R2，光敏三极管的发射极与芯片接地端GND连接；发光二极管与光敏三极管组成光耦合器OE1。The RXD circuit on the chip side includes: the chip RXD receiving port, the voltage source VCC, the second resistor R2, and the phototransistor; the chip RXD input port is connected to the collector of the phototransistor, and the second resistor is connected in series between the collector of the phototransistor and the voltage source VCC R2, the emitter of the phototransistor is connected to the ground terminal GND of the chip; the light emitting diode and the phototransistor form an optical coupler OE1.

其中，电压源VCC为3.3V。Wherein, the voltage source VCC is 3.3V.

计算机通过计算机TXD发送端口发送信号，芯片通过芯片RXD接收端口接收信号。当计算机TXD发送端口发送的是高电平+12V的信号时，第一二极管D1截止，发光二极管不发光，光敏三极管不导通，芯片RXD接收端口接收到的为电压源VCC供电的高电平3.3V。当计算机TXD发送端口发送的是低电平-12V时，第一二极管D1导通，发光二极管发光，光敏三极管导通，芯片RXD接收端口接收到的为低电平。这样就实现了+12V到3.3V和-12V到TTL低电平的转换。The computer sends signals through the computer TXD sending port, and the chip receives signals through the chip RXD receiving port. When the TXD sending port of the computer sends a high-level +12V signal, the first diode D1 is cut off, the light-emitting diode does not emit light, and the photosensitive transistor is not turned on. Level 3.3V. When the TXD sending port of the computer sends a low level -12V, the first diode D1 is turned on, the light-emitting diode emits light, the phototransistor is turned on, and the RXD receiving port of the chip receives a low level. In this way, the conversion of +12V to 3.3V and -12V to TTL low level is realized.

实施例3Example 3

如图4所示，一种具有隔离功能的RS232接口保护电路，包括计算机侧RXD电路和芯片侧TXD电路；As shown in Figure 4, a RS232 interface protection circuit with isolation function includes a computer side RXD circuit and a chip side TXD circuit;

芯片侧TXD电路包含：芯片TXD发送端口、第一三极管Q1、第二三极管Q2、第一电流变压器T1、第二电流变压器T2、第四电阻R4、第六电阻R6、电压源VCC；第一三极管Q1为PN P晶体管，第二三极管Q2为NPN晶体管；The TXD circuit on the chip side includes: chip TXD sending port, first transistor Q1, second transistor Q2, first current transformer T1, second current transformer T2, fourth resistor R4, sixth resistor R6, voltage source VCC ; The first triode Q1 is a PPN P transistor, and the second triode Q2 is an NPN transistor;

芯片TXD发送端口分别连接第一三极管Q1的基极和第二三极管Q2的基极；电源源VCC与第一三极管Q1的发射极之间依次串联第四电阻和第一电流变压器的低压侧，第一三极管Q1的集电极与接地端GND连接；The sending port of the chip TXD is respectively connected to the base of the first transistor Q1 and the base of the second transistor Q2; the fourth resistor and the first current are connected in series between the power source VCC and the emitter of the first transistor Q1 On the low-voltage side of the transformer, the collector of the first triode Q1 is connected to the ground terminal GND;

电源源VCC与第二三极管Q2的集电极依次串联第六电阻、第二电流变压器的低压侧，第二三极管Q2的发射极与芯片接地端GND连接。The power source VCC and the collector of the second transistor Q2 are connected in series with the sixth resistor and the low-voltage side of the second current transformer, and the emitter of the second transistor Q2 is connected to the chip ground terminal GND.

计算机侧RXD电路包含：计算机RXD接收端口、第三电阻R3、第五电阻R5、第二二极管D2、第三二极管D3；计算机RXD接收端口分别连接第一电流变压器T1的高压侧线圈的负极端和第二电流变压器T2的高压侧线圈的正极端；The RXD circuit on the computer side includes: the computer RXD receiving port, the third resistor R3, the fifth resistor R5, the second diode D2, and the third diode D3; the computer RXD receiving port is respectively connected to the high-voltage side coil of the first current transformer T1 and the positive terminal of the high voltage side coil of the second current transformer T2;

第一电流变压器T1的高压侧线圈的正极端与计算机信号GND之间依次串联第三电阻R3和第二二极管D2，第二二极管D2的阳极与计算机信号GND连接。A third resistor R3 and a second diode D2 are connected in series between the positive end of the high voltage side coil of the first current transformer T1 and the computer signal GND, and the anode of the second diode D2 is connected to the computer signal GND.

第二电流变压器T2的高压侧线圈的负极端与计算机信号GND之间依次串联第五电阻R5和第三二极管D3，第三二极管D3的阴极与计算机信号GND连接。A fifth resistor R5 and a third diode D3 are connected in series between the negative end of the high voltage side coil of the second current transformer T2 and the computer signal GND, and the cathode of the third diode D3 is connected to the computer signal GND.

其中，电压源VCC为3.3V；第一电流变压器T1的电压转换比为3:1，其高压侧线圈和低压侧线圈绕向一致；第二电流变压器T2的电压转换比也为3:1，其高压侧线圈和低压侧线圈绕向也一致。Among them, the voltage source VCC is 3.3V; the voltage conversion ratio of the first current transformer T1 is 3:1, and the winding direction of the high-voltage side coil and the low-voltage side coil are consistent; the voltage conversion ratio of the second current transformer T2 is also 3:1, The high-voltage side coil and the low-voltage side coil also have the same winding direction.

芯片通过芯片TXD发送端口发送信号，计算机通过计算机RXD接收端口接收信号。芯片TXD发送端口的电平为TTL电平，计算机RXD接收端口符合RS232电平规范。在无信号传输时，芯片TXD发送端口为TTL高电平计算机RXD接收端口按规范为TTL高点平或低电平，具体状态由其内部电路决定。此状态不影响信号传输过程。The chip sends signals through the chip TXD sending port, and the computer receives signals through the computer RXD receiving port. The level of the TXD sending port of the chip is TTL level, and the RXD receiving port of the computer complies with the RS232 level specification. When there is no signal transmission, the TXD sending port of the chip is TTL high level, and the computer RXD receiving port is TTL high level or low level according to the specification, and the specific state is determined by its internal circuit. This state does not affect the signaling process.

当芯片TXD发送端口为TTL高电平时，第一三极管Q1截止、第二三极管Q2导通，第一电流变压器T1中无电流，第二电流变压器T2中有电流，第二二极管D2截止，第三二极管D3导通，计算机RXD接收端口为RS232高电平+12V，这样就实现了TTL高电平到RS232高电平的转换。When the sending port of the chip TXD is at TTL high level, the first triode Q1 is turned off, the second triode Q2 is turned on, there is no current in the first current transformer T1, there is current in the second current transformer T2, and the second diode The tube D2 is cut off, the third diode D3 is turned on, and the RXD receiving port of the computer is RS232 high level +12V, thus realizing the conversion from TTL high level to RS232 high level.

当芯片TXD发送端口为TTL低电平时，第一三极管Q1导通、第二三极管Q2截止，第二电流变压器T2中无电流，第一电流变压器T1中有电流，第三二极管D3截止，第二二极管D2导通，计算机RXD接收端口为RS232低电平-12V，这样就实现了TTL低电平到RS232低电平的转换。When the sending port of the chip TXD is at TTL low level, the first transistor Q1 is turned on, the second transistor Q2 is turned off, there is no current in the second current transformer T2, there is current in the first current transformer T1, and the third diode The tube D3 is cut off, the second diode D2 is turned on, and the RXD receiving port of the computer is RS232 low level -12V, thus realizing the conversion from TTL low level to RS232 low level.

图2、图3和图4中，第一电阻R1、第二电阻R2、第三电阻R3、第四电阻R4、第五电阻R5、第六电阻R6、第七电阻R7、第八电阻R8、第九电阻R8是限流电阻，可以根据实际的应用环境选择不同的阻值，以调节对应回路的电流大小，进而调节RXD接收端口电平变化的快慢程度。合理的选择电流变压器的绕组匝数也可以调节RXD接收端口RXD电平变化的快慢程度。In Fig. 2, Fig. 3 and Fig. 4, the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, the seventh resistor R7, the eighth resistor R8, The ninth resistor R8 is a current-limiting resistor. Different resistance values can be selected according to the actual application environment to adjust the current of the corresponding loop, and then adjust the speed of the RXD receiving port level change. Reasonable selection of the winding turns of the current transformer can also adjust the speed of RXD level change at the RXD receiving port.

应该指出，图中的器件和参数只是示例性，同等替换都在本申请的保护范围之内；同等功能的器件替代也在本专利的保护范围之内。It should be pointed out that the devices and parameters in the figure are only exemplary, and equivalent replacements are within the protection scope of this application; device replacements with equivalent functions are also within the protection scope of this patent.

虽然，本说明书中已经用一般性说明及具体实施方案对本发明作了详尽的描述，但在本发明基础上，可以对之作一些修改或改进，这对本领域技术人员而言是显而易见的。因此，在不偏离本发明精神的基础上所做的这些修改或改进，均属于本发明要求保护的范围。Although the present invention has been described in detail with general descriptions and specific embodiments in this specification, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.