CN115562249A - Differential bus system for automobile diagnosis - Google Patents
Differential bus system for automobile diagnosis Download PDFInfo
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- CN115562249A CN115562249A CN202211393569.XA CN202211393569A CN115562249A CN 115562249 A CN115562249 A CN 115562249A CN 202211393569 A CN202211393569 A CN 202211393569A CN 115562249 A CN115562249 A CN 115562249A
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B23/00—Testing or monitoring of control systems or parts thereof
- G05B23/02—Electric testing or monitoring
- G05B23/0205—Electric testing or monitoring by means of a monitoring system capable of detecting and responding to faults
- G05B23/0208—Electric testing or monitoring by means of a monitoring system capable of detecting and responding to faults characterized by the configuration of the monitoring system
- G05B23/0213—Modular or universal configuration of the monitoring system, e.g. monitoring system having modules that may be combined to build monitoring program; monitoring system that can be applied to legacy systems; adaptable monitoring system; using different communication protocols
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- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B2219/00—Program-control systems
- G05B2219/20—Pc systems
- G05B2219/24—Pc safety
- G05B2219/24065—Real time diagnostics
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Abstract
The invention discloses a differential bus system for automobile diagnosis, which comprises a main control MCU circuit, an adjustable differential bus circuit and an OBD diagnosis interface which are connected in sequence, wherein the main control MCU circuit outputs or receives square wave pulses, the adjustable differential bus circuit comprises a differential bus high-end transmitting circuit and a differential bus low-end transmitting circuit, the main control MCU circuit is connected with the differential bus high-end transmitting circuit and the differential bus low-end transmitting circuit in parallel, the differential bus high-end transmitting circuit and the differential bus low-end transmitting circuit are respectively connected with the OBD diagnosis interface, data stream transmission between the main control MCU circuit and the OBD diagnosis interface is realized by utilizing voltage difference change simulation of the differential bus high-end transmitting circuit and the differential bus low-end transmitting circuit, finally, the function of fault finding or diagnosis of an automobile is realized, the problem that the automobile with the adjustable differential bus cannot be diagnosed by the existing automobile diagnosis instrument is solved, the use scene of the diagnosis instrument is expanded, and the universality of the diagnosis instrument is improved.
Description
Technical Field
The invention relates to the technical field of automobile diagnosis, in particular to a differential bus system for automobile diagnosis.
Background
The automobile bus is a channel for data exchange between an automobile ECU and each control unit of an automobile, the current general automobile bus mainly comprises a K line, an RS485 line, an RS232 line, a J1850 line, a single-wire CAN line, a low-speed CAN line, a high-speed CAN line, a CANFD line, an automobile Ethernet and the like, and the automobile bus has the biggest characteristic that stable and reliable data signals CAN be transmitted by using the fewest wire harnesses, and meanwhile, along with the improvement of the technology, the transmission speed is faster and faster, and more information is contained in bus data streams. Because of various bus forms, the bus forms adopted by various automobile manufacturers are different, and different bus forms can be adopted by different automobile models of the same automobile manufacturer according to the technical characteristics of the same automobile manufacturer. In order to protect the automobile ECU data and prevent the ECU data from being illegally rewritten or read, different automobile manufacturers establish a non-standard bus standard, namely an adjustable differential bus by themselves.
However, although the way of setting the adjustable differential bus in the automobile prevents the ECU data from being illegally rewritten or read, it has a significant disadvantage that the existing diagnostic device cannot check the automobile with the adjustable differential bus, and once the automobile with the adjustable differential bus fails, the ordinary diagnostic device cannot normally read the state of the ECU from the OBD diagnostic port, which brings inconvenience to the automobile maintenance.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a differential bus system for automobile diagnosis, which solves the problem that the existing automobile diagnosis instrument cannot carry out automobile diagnosis on an automobile with an adjustable differential bus, enlarges the use scene of the diagnosis instrument, improves the universality of the diagnosis instrument and overcomes the defects of the prior art.
In order to solve the above technical problems, the present invention provides a differential bus system for automobile diagnosis, which comprises a main control MCU circuit, an adjustable differential bus circuit and an OBD diagnosis interface connected in sequence,
the master control MCU circuit comprises two paths of IO interfaces, wherein one path of IO interface is an output IO interface for outputting square wave pulses, and the other path of IO interface is an input IO interface for receiving the square wave pulses;
the adjustable differential bus circuit comprises a differential bus high-end transmitting circuit, a differential bus low-end transmitting circuit, a differential bus matching terminal and a differential bus receiving circuit, wherein an output IO interface of the master control MCU circuit is connected with input interfaces of the differential bus high-end transmitting circuit and the differential bus low-end transmitting circuit in parallel, the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit are respectively connected with the OBD diagnosis interface, the differential bus matching terminal is connected between the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit, and the differential bus receiving circuit receives differential signals output by the adjustable differential bus circuit and transmits the differential signals to the input IO interface of the master control MCU circuit.
When the main control MCU circuit has no data output, the voltage of the output interface of the differential bus high-end transmitting circuit and the voltage of the output interface of the differential bus low-end transmitting circuit are equal, the voltage difference is 0, and the voltage difference on the adjustable differential bus circuit represents the binary number 0 in the data stream; when the main control MCU circuit has data output, a voltage difference V exists between the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit, at the moment, the voltage difference V on the adjustable differential bus circuit represents binary number 1 in the data stream, and the binary data in the data stream is simulated through the voltage difference of the adjustable differential bus circuit, so that the data stream transmission from the output IO interface of the main control MCU circuit to the OBD diagnosis interface is realized.
As an improvement of the present invention, the differential bus matching terminal includes a termination resistor R5, one end of the termination resistor R5 is connected to the output interface of the high-side transmitting circuit of the differential bus, and the other end is connected to the output interface of the low-side transmitting circuit of the differential bus, and the termination resistor R5 is used for improving the differential signal transmission waveform and reducing the high-speed signal reflection.
As a further improvement of the present invention, the differential bus high-end transmitting circuit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a triode Q1, a triode Q2, a safety resistor F1, and at least one diode D1, wherein one end of the resistor R2 is connected to an output IO interface of the main control MCU circuit, the other end of the resistor R2 is connected in parallel with one end of the resistor R3 and a base of the triode Q2, and the other end of the resistor R3 is connected in parallel with an emitter of the triode Q2 and one end of the resistor R4 and then connected to a ground GND; the collector of the triode Q2 is connected with one end of the resistor R1, and the other end of the resistor R1 is connected with the base of the triode Q1; an emitting electrode of the triode Q1 is connected with one end of a safety resistor F1, and the other end of the safety resistor F1 is connected to a power input end VCCIN; the collector of the triode Q1 is connected in parallel with the other end of the resistor R4 and the anode of the diode D1; the cathode of the diode D1 is connected in parallel with one end of the terminal resistor R5, and the cathode of the diode D1 is connected to the output interface of the differential bus high-end sending circuit.
As an improvement of the present invention, when the output IO interface of the main control MCU circuit outputs a low level, the voltage applied to the base of the transistor Q2 is a low level after voltage division by the resistor R2 and the resistor R3, at this time, the transistor Q2 is turned off, the transistor Q2 is in an open circuit state, and at the same time, the transistor Q1 is in an open circuit state, the anode of the diode D1 is at a zero level, at this time, the voltage of the output interface in the differential bus high-side transmitting circuit is in a static state, and the voltage of the output interface in the differential bus high-side transmitting circuit is V _ OUT; when the output IO interface of the main control MCU circuit outputs high level, after voltage division is carried OUT through a resistor R2 and a resistor R3, the voltage added to the base electrode of the triode Q2 is high level, the base electrode of the triode Q2 is in forward bias conduction, the collector electrode level of the triode Q2 is equal to the ground end GND, the base electrode of the triode Q1 is low level, the triode Q1 is in a conduction state, the collector electrode voltage of the triode Q1 is equal to the power input end VCCIN, the diode D1 is in forward conduction because the power input end VCCIN is larger than V _ OUT, the diode D1 is in forward conduction, the cathode voltage of the diode D1 is VCCIN-P because the forward voltage drop of the diode D1 is a constant value P, and the voltage of the output interface in the differential bus high-end sending circuit is increased to VCCIN-P.
As a further improvement of the present invention, the differential bus low-end transmitting circuit includes a resistor R6, a resistor R7, a transistor Q3, and at least one diode D2, wherein one end of the resistor R6 is connected to an output IO interface of the main control MCU circuit, and the other end of the resistor R6 is connected in parallel with one end of the resistor R7 and a base of the transistor Q3; the other end of the resistor R7 is connected with an emitting electrode of the triode Q3, and meanwhile, the other end of the resistor R7 is connected to a ground end GND in parallel; the collector of the triode Q3 is connected with one end of a resistor R9, and the collector of the triode Q3 is connected to the negative electrode of a diode D2 in parallel; the anode of the diode D2 is connected in parallel with the other end of the termination resistor R5, and the anode of the diode D2 is connected to the output interface of the low-side transmitting circuit of the differential bus.
As an improvement of the present invention, when the output IO interface of the main control MCU circuit outputs a low level, after voltage division is performed by the resistor R6 and the resistor R7, the voltage applied to the base of the transistor Q3 is a low level, at this time, the transistor Q3 is turned off, and the transistor Q3 is in an open circuit state, so that the cathode of the diode D2 is in an open circuit state, and since the levels of the output interfaces of the differential bus high-side transmitting circuit and the differential bus low-side transmitting circuit are kept equal in a static state of the adjustable differential bus circuit, the voltage of the output interface in the differential bus high-side transmitting circuit is V _ OUT; when the output IO interface of the main control MCU circuit outputs high level, after voltage division is carried out through the resistor R6 and the resistor R7, the voltage added to the base electrode of the triode Q3 is high level, the forward bias of the triode Q3 is conducted at the moment, the voltage of the collector electrode of the triode Q3 is equal to the ground end GND, namely, the voltage of the cathode of the diode D2 is equal to the ground end GND at the moment, the forward voltage drop of the single diode D2 is a constant value P, the voltage is pulled down to P through the anode of the diode D2, and therefore the voltage of the output interface in the differential bus low-end sending circuit is pulled down to P.
As an improvement of the present invention, when the main control MCU circuit has no data transmission, the voltages of the output interfaces of the differential bus high-side transmitting circuit and the differential bus low-side transmitting circuit are both V _ OUT, at this time, the voltage difference on the adjustable differential bus circuit is 0, and at this time, the voltage difference represents a binary number 0 in the data stream; when the master control MCU circuit transmits data, the voltage of the output interface of the low-end transmitting circuit of the differential bus is VCCIN-P, and the voltage of the output interface of the low-end transmitting circuit of the differential bus is P, so that the voltage difference V = VCCIN-2P between the voltage of the high-end differential bus and the voltage of the low-end differential bus, at the moment, the voltage difference V on the adjustable differential bus circuit represents binary number 1 in data stream, and the data transmission process from the output IO interface of the master control MCU circuit to the OBD diagnosis interface is realized through the voltage difference change of the adjustable differential bus circuit.
As a further improvement of the present invention, the differential bus receiving circuit includes a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, and a comparator U1A, where one end of the resistor R9 is connected to the cathode of the diode D2, and the other end of the resistor R9 is connected to the 2 nd pin of the comparator U1A; one end of the resistor R11 is connected to a power supply input end VCCIN, and the other end of the resistor R11 is connected with one end of the resistor R12 and the 3 rd pin of the comparator U1A in parallel; the other end of the resistor R12 is connected in parallel with a 4 th pin of the comparator U1A and then connected to a ground end GND, and an 8 th pin of the comparator U1A is connected to a power supply input end VCCIN; one end of the resistor R8 is connected with a power supply VCC3V3, the other end of the resistor R8 is connected with the 1 st pin of the comparator U1A and one end of the resistor R10 in parallel, and the other end of the resistor R10 is connected to an input IO interface of the master control MCU circuit.
As a further improvement of the present invention, when the binary data transmitted by the adjustable differential bus circuit is 1, the transistor Q3 in the low-side transmitting circuit of the differential bus is in a conducting state, and at this time, the voltage of the cathode of the diode D2 in the low-side transmitting circuit of the differential bus is P, and the voltage of the cathode of the diode D2 is loaded to the 2 nd pin of the comparator U1A through the resistor R9, because the voltage of the 3 rd pin of the comparator U1A is greater than the voltage of the 2 nd pin of the comparator U1A, the 1 st pin of the comparator U1A outputs a high level, and is connected to the input IO interface of the main control MCU circuit through the resistor R10, so that the input IO interface of the main control MCU circuit is a high level, and the input IO interface of the main control MCU circuit receives the binary data 1; when the binary data transmitted by the adjustable differential bus circuit is 0, the triode Q3 in the differential bus low-end transmitting circuit is in a cut-off state, at this time, the cathode voltage of the diode D2 of the differential bus low-end transmitting circuit is equal to the voltage V _ OUT of the output interface of the differential bus low-end transmitting circuit, the cathode voltage of the diode D2 is loaded to the 2 nd pin of the comparator U1A through the resistor R9, at this time, the voltage of the 3 rd pin of the comparator U1A is smaller than the voltage of the 2 nd pin of the comparator U1A, so that the 1 st pin of the comparator U1A outputs a low level and is connected to the input interface of the main control MCU circuit through the resistor IO 10, the input IO interface of the main control MCU circuit is a low level, and the input IO interface of the main control MCU circuit receives the binary data 0.
As a further improvement of the present invention, the resistance values of the resistor R11 and the resistor R12 are obtained according to the formula R12 ÷ (R11 + R12) xvcin = V _ OUT/2, so that after voltage division is performed by the resistor R12 and the resistor R11, the voltage of the 3 rd pin of the comparator U1A is equal to half of the voltage of the output interface of the differential bus high-side transmitter circuit or the differential bus low-side transmitter circuit in the static state.
After adopting such design, the invention has at least the following advantages:
(1) The invention provides the adjustable differential bus system which can be used in the diagnostic instrument, so that the diagnostic instrument can carry out fault finding or diagnosis on the vehicle adopting the adjustable differential bus through the OBD diagnostic interface, thereby ensuring that maintenance personnel can quickly and accurately judge the vehicle state, quickly and efficiently detecting and maintaining the vehicle fault and state adopting the adjustable differential bus circuit, bringing convenience to vehicle maintenance and improving the maintenance efficiency.
(2) The adjustable differential bus circuit realizes data stream output from the main control MCU circuit by utilizing voltage difference change simulation of the differential bus high-end transmitting circuit and the differential bus low-end transmitting circuit, and transmits the data stream to the OBD diagnosis interface through the adjustable differential bus circuit, thereby realizing data stream transmission between the main control MCU circuit and the OBD diagnosis interface and further realizing the function of carrying out fault finding or diagnosis on the automobile.
Drawings
The foregoing is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and the detailed description.
Fig. 1 is a schematic structural diagram of a differential bus system for automobile diagnosis according to an embodiment of the present invention.
Fig. 2 is a schematic circuit diagram of a differential bus system according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of an adjustable differential bus circuit according to an embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a differential bus high-side transmission circuit according to an embodiment of the present invention.
Fig. 5 is a schematic structural diagram of a differential bus low-side transmitter circuit according to an embodiment of the present invention.
Fig. 6 is a schematic structural diagram of a differential bus receiving circuit according to an embodiment of the present invention.
Detailed Description
Examples of the embodiments described herein are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar parts throughout, or parts having the same or similar functions. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention and are not to be construed as limiting the present invention.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, or can be communicated between the two components. The specific meanings of the above terms in the present invention can be understood as specific cases by those skilled in the art.
Referring to fig. 1, a differential bus system for vehicle diagnosis is specifically disclosed in this embodiment, which includes a main control MCU circuit, an adjustable differential bus circuit, and an OBD diagnosis interface, which are connected in sequence.
Specifically, the main control MCU circuit includes two paths of IO interfaces, one of the IO interfaces is an output IO interface for outputting square wave pulses, and the other of the IO interfaces is an input IO interface for receiving square wave pulses. And two paths of IO interfaces in the main control MCU circuit are used for data transmission and data reception.
With reference to fig. 2 and fig. 3, the adjustable differential bus circuit includes a differential bus high-side transmitting circuit, a differential bus low-side transmitting circuit, a differential bus matching terminal, and a differential bus receiving circuit, where the adjustable differential bus circuit is mainly used to convert pulses sent by the main control MCU circuit into one high-side pulse signal and one low-side pulse signal, so as to form a differential signal form, and the adjustable differential bus circuit is connected to the OBD diagnostic interface and sends a data stream for diagnosis to the OBD diagnostic interface in a differential signal manner. Meanwhile, the adjustable differential bus circuit also inputs the differential signal data stream in the adjustable differential bus circuit into the main control MCU circuit through the differential bus receiving circuit for diagnosis of the vehicle.
Wherein the output IO interface parallel connection difference bus high-end transmitting circuit of master control MCU circuit and the input interface of difference bus low side transmitting circuit, the output interface of difference bus high-end transmitting circuit and the output interface of difference bus low side transmitting circuit connect respectively OBD diagnoses the interface, just connect between the output interface of difference bus high-end transmitting circuit and the output interface of difference bus low side transmitting circuit difference bus matching terminal, difference bus receiving circuit receives the difference signal of adjustable difference bus circuit output and transmits to the input IO interface of master control MCU circuit.
When the main control MCU circuit has no data output, the voltage of the output interface of the differential bus high-end transmitting circuit and the voltage of the output interface of the differential bus low-end transmitting circuit are equal, the voltage difference is 0, and the voltage difference on the adjustable differential bus circuit represents the binary number 0 in the data stream; when the master control MCU circuit outputs data, a voltage difference V exists between the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit, the voltage difference V on the adjustable differential bus circuit represents binary number 1 in the data stream, and the binary data in the data stream is simulated through the voltage difference of the adjustable differential bus circuit, so that the data stream transmission from the output IO interface of the master control MCU circuit to the OBD diagnosis interface is realized.
The differential bus matching terminal comprises a terminal resistor R5, one end of the terminal resistor R5 is connected to an output interface of the differential bus high-end transmitting circuit, the other end of the terminal resistor R5 is connected to an output interface of the differential bus low-end transmitting circuit, and the terminal resistor R5 is used for improving the transmission waveform of differential signals and reducing high-speed signal reflection. The value of the termination resistor R5 in this embodiment is preferably 100 ohms.
As shown in fig. 4, the differential bus high-end transmitting circuit includes a resistor R1, a resistor R2, a resistor R3, a resistor R4, a triode Q1, a triode Q2, a safety resistor F1, and at least one diode D1, and in this embodiment, preferably, the resistor R1 and the resistor R2 take 4.7K ohms, the resistor R3 takes 10K ohms, the resistor R4 takes 1K ohms, the triode Q1 takes MMBT3906, the triode Q2 takes MMBT3904W, the diode D1 takes SS14, and the safety resistor F1 takes 0.1A/60 as a parameter.
Specifically, one end of the resistor R2 is connected to an output IO interface of the main control MCU circuit, the other end of the resistor R2 is connected in parallel with one end of the resistor R3 and a base of the transistor Q2, and the other end of the resistor R3 is connected in parallel with an emitter of the transistor Q2 and one end of the resistor R4 and then connected to a ground GND; the collector of the triode Q2 is connected with one end of the resistor R1, and the other end of the resistor R1 is connected with the base of the triode Q1; an emitting electrode of the triode Q1 is connected with one end of a safety resistor F1, and the other end of the safety resistor F1 is connected to a power input end VCCIN; the collector of the triode Q1 is connected in parallel with the other end of the resistor R4 and the anode of the diode D1; the cathode of the diode D1 is connected in parallel with one end of the terminal resistor R5, and the cathode of the diode D1 is connected to the output interface OUT-P of the differential bus high-end sending circuit.
The working process of the differential bus high-end sending circuit is as follows:
when the output IO interface of the main control MCU circuit outputs a low level, after voltage division is performed by the resistors R2 and R3, the voltage applied to the base of the transistor Q2 is a low level, at this time, the transistor Q2 is turned off, the transistor Q2 is in an open circuit state, and at the same time, the transistor Q1 is in an open circuit state, the anode of the diode D1 is a zero level, at this time, the diode D1 is in a reverse cut-off state, because the voltage of the output interface in the differential bus high-end transmitting circuit is in a static state, the voltage thereof is maintained at a constant value, in this embodiment, the voltage of the output interface in the differential bus high-end transmitting circuit is set to be V _ OUT, that is, the voltage of the output interface in the differential bus high-end transmitting circuit is V _ OUT. It should be noted that the actual voltage of V _ OUT is related to the vehicle type, based on the measured value of the vehicle.
When the output IO interface of the main control MCU circuit outputs high level, after voltage division is carried OUT through the resistor R2 and the resistor R3, the voltage added to the base electrode of the triode Q2 is high level, the base electrode of the triode Q2 is conducted in forward bias mode, the collector electrode level of the triode Q2 is basically equal to the ground end GND, the base electrode of the triode Q1 is low level, the triode Q1 is in a conducting state, the collector electrode voltage of the triode Q1 is basically equal to the power input end VCCIN, the diode D1 is conducted in forward direction because the power input end VCCIN is larger than V _ OUT, the diode D1 is in forward direction, the cathode voltage of the diode D1 is VCCIN-P because the forward voltage drop of the diode D1 is a constant value P, and the voltage of the output interface in the differential bus high-end sending circuit is increased to be VCCIN-P at the moment. For example, if the forward voltage drop of the diode D1 is a constant value of 0.3V, the voltage of the cathode of the diode D1 is VCCIN-0.3V after the power input terminal VCCIN passes through the diode D1, and since VCCIN-0.3V is much larger than V _ OUT, the voltage of the output interface in the high-side transmitting circuit of the differential bus will be increased to VCCIN-0.3V.
Referring to fig. 5, the differential bus low-side transmitting circuit in this embodiment includes a resistor R6, a resistor R7, a transistor Q3, and at least one diode D2. In this embodiment, it is preferable that the resistor R6 has a value of 4.7 kohm, the resistor R7 has a value of 10 kohm, the triode Q3 is MMBT3904W, and the diode D2 is SS14.
Specifically, one end of the resistor R6 is connected to an output IO interface of the main control MCU circuit, and the other end of the resistor R6 is connected in parallel with one end of the resistor R7 and the base of the triode Q3; the other end of the resistor R7 is connected with an emitting electrode of the triode Q3, and meanwhile, the other end of the resistor R7 is connected to a ground end GND in parallel; the collector of the triode Q3 is connected with one end of a resistor R9, and the collector of the triode Q3 is connected to the negative electrode of a diode D2 in parallel; the anode of the diode D2 is connected in parallel with the other end of the termination resistor R5, and the anode of the diode D2 is connected to the output interface OUT-N of the low-side transmitting circuit of the differential bus.
The working process of the differential bus low-side transmitting circuit is as follows:
when the output IO interface of the main control MCU circuit outputs a low level, after voltage division is performed by the resistor R6 and the resistor R7, the voltage applied to the base of the transistor Q3 is a low level, at this time, the transistor Q3 is turned off, and the transistor Q3 is in an open circuit state, so that the cathode of the diode D2 is in an open circuit state, since the levels of the output interfaces of the differential bus high-side transmitting circuit and the differential bus low-side transmitting circuit of the adjustable differential bus circuit in a static state are kept equal, the voltage of the output interface in the differential bus high-side transmitting circuit is V _ OUT, and the voltage difference between the differential bus high-side transmitting circuit and the differential bus low-side transmitting circuit in the adjustable differential bus circuit is 0. It should be noted that the actual voltage of V _ OUT is related to the vehicle type, based on the measured value of the vehicle.
When the output IO interface of the main control MCU circuit outputs high level, after voltage division is carried out through the resistor R6 and the resistor R7, the voltage added to the base electrode of the triode Q3 is high level, the forward bias of the triode Q3 is conducted at the moment, the voltage of the collector electrode of the triode Q3 is equal to the ground end GND, namely the voltage of the cathode of the diode D2 is equal to the ground end GND at the moment, the forward voltage drop of the single diode D2 is a constant value P, so that the voltage is pulled down to P through the anode of the diode D2, and finally the voltage of the output interface in the low-end transmitting circuit of the differential bus is pulled down to P.
In this embodiment, when the master control MCU circuit has no data transmission, that is, the output IO interface of the master control MCU circuit outputs a low level, the voltages of the output interfaces of the differential bus high-side transmitting circuit and the differential bus low-side transmitting circuit are both V _ OUT, the voltage difference on the adjustable differential bus circuit is 0, and the voltage difference represents a binary number 0 in the data stream; when the master control MCU circuit transmits data, namely the output IO interface of the master control MCU circuit outputs high level, the voltage of the output interface of the low-end transmitting circuit of the differential bus is VCCIN-P, and the voltage of the output interface of the low-end transmitting circuit of the differential bus is P, therefore, the voltage difference V between the voltage of the high-end differential bus and the voltage of the low-end differential bus is = VCCIN-2P, the voltage difference V on the adjustable differential bus circuit represents binary number 1 in data stream, and the data transmission process from the output IO interface of the master control MCU circuit to the OBD diagnosis interface is realized through the voltage difference change of the adjustable differential bus circuit.
Further, referring to fig. 6, the differential bus receiving circuit in this embodiment includes a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12, and a comparator U1A. In this embodiment, preferably, the resistor R8 is 4.7K ohms, the resistor R9 is 10K ohms, the resistor R10 is 1K ohms, and the resistance values of the resistor R11 and the resistor R12 are according to the following formula:
R12÷(R11+R12)xVCCIN＝V_OUT/2；
the values of the resistor R11 and the resistor R12 are obtained according to the above formula, so that after voltage division is performed by the resistor R12 and the resistor R11, the voltage of the 3 rd pin of the comparator U1A is equal to half of the output interface voltage of the differential bus high-end transmitting circuit or the differential bus low-end transmitting circuit in the static state, in this embodiment, the resistor R11 is preferably an 18K resistor, and the resistor R12 is preferably a 2K resistor.
Specifically, one end of the resistor R9 is connected to the cathode of the diode D2, and the other end of the resistor R9 is connected to the 2 nd pin of the comparator U1A; one end of the resistor R11 is connected to a power supply input end VCCIN, and the other end of the resistor R11 is connected with one end of the resistor R12 and the 3 rd pin of the comparator U1A in parallel; the other end of the resistor R12 is connected in parallel with a 4 th pin of the comparator U1A and then connected to a ground end GND, and an 8 th pin of the comparator U1A is connected to a power supply input end VCCIN; one end of the resistor R8 is connected with a power supply VCC3V3, the other end of the resistor R8 is connected with the 1 st pin of the comparator U1A and one end of the resistor R10 in parallel, and the other end of the resistor R10 is connected to an input IO interface of the master control MCU circuit. The differential bus receiving circuit is mainly used for receiving differential signal data streams transmitted by the adjustable differential bus circuit and transmitting the differential signal data streams to the main control MCU circuit, so that the diagnostic apparatus can perform automobile fault analysis according to the differential signal data streams.
The working process of the differential bus receiving circuit is as follows:
when the design is carried OUT, a voltage value V _ OUT/2 is obtained by dividing the voltage of a resistor R12 and a resistor R11, so that the voltage of a 3 rd pin of an integrated comparator U1A is also V _ OUT/2, when binary data transmitted by an adjustable differential bus circuit is 1, a triode Q3 in a low-end transmitting circuit of a differential bus is in a conducting state, the voltage of a cathode of a diode D2 in the low-end transmitting circuit of the differential bus is P, the voltage of a cathode of the diode D2 is loaded to a 2 nd pin of the comparator U1A through a resistor R9, and because the voltage of the 3 rd pin of the comparator U1A is greater than the voltage of the 2 nd pin of the comparator U1A, the 1 st pin of the comparator U1A outputs a high level and is connected to an input IO interface of a master control MCU circuit through a resistor R10, so that the IO interface of the master control MCU circuit is a high level, the input interface of the master control MCU circuit receives the binary data 1;
when the binary data transmitted by the adjustable differential bus circuit is 0, the triode Q3 in the differential bus low-side transmitting circuit is in a cut-off state, at this time, the cathode voltage of the diode D2 of the differential bus low-side transmitting circuit is equal to the voltage V _ OUT of the output interface of the differential bus low-side transmitting circuit, the cathode voltage of the diode D2 is loaded to the 2 nd pin of the comparator U1A through the resistor R9, at this time, the 3 rd pin voltage of the comparator U1A is smaller than the 2 nd pin voltage of the comparator U1A, so that the 1 st pin of the comparator U1A outputs a low level and is connected to the input interface of the main control MCU circuit through the resistor IO 10, the input IO interface of the main control MCU circuit is a low level, and then the input IO interface of the main control MCU circuit receives the binary data 0.
While the invention has been described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (10)
1. A differential bus system for automobile diagnosis is characterized by comprising a main control MCU circuit, an adjustable differential bus circuit and an OBD diagnosis interface which are connected in sequence,
the master control MCU circuit comprises two paths of IO interfaces, wherein one path of IO interface is an output IO interface for outputting square wave pulses, and the other path of IO interface is an input IO interface for receiving the square wave pulses;
the adjustable differential bus circuit comprises a differential bus high-end transmitting circuit, a differential bus low-end transmitting circuit, a differential bus matching terminal and a differential bus receiving circuit, wherein an output IO interface of the master control MCU circuit is connected with input interfaces of the differential bus high-end transmitting circuit and the differential bus low-end transmitting circuit in parallel, the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit are respectively connected with the OBD diagnosis interface, the differential bus matching terminal is connected between the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit, and the differential bus receiving circuit receives differential signals output by the adjustable differential bus circuit and transmits the differential signals to the input IO interface of the master control MCU circuit;
when the main control MCU circuit has no data output, the voltage of the output interface of the differential bus high-end transmitting circuit and the voltage of the output interface of the differential bus low-end transmitting circuit are equal, the voltage difference is 0, and the voltage difference on the adjustable differential bus circuit represents the binary number 0 in the data stream; when the master control MCU circuit outputs data, a voltage difference V exists between the output interface of the differential bus high-end transmitting circuit and the output interface of the differential bus low-end transmitting circuit, the voltage difference V on the adjustable differential bus circuit represents binary number 1 in the data stream, and the binary data in the data stream is simulated through the voltage difference of the adjustable differential bus circuit, so that the data stream transmission from the output IO interface of the master control MCU circuit to the OBD diagnosis interface is realized.
2. The differential bus system as recited in claim 1, wherein the differential bus matching terminal comprises a termination resistor R5, one end of the termination resistor R5 is connected to the output interface of the differential bus high-side transmitter circuit, and the other end is connected to the output interface of the differential bus low-side transmitter circuit, and the termination resistor R5 is used for improving the differential signal transmission waveform and reducing the high-speed signal reflection.
3. The differential bus system as claimed in claim 2, wherein the differential bus high-side transmitting circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a transistor Q1, a transistor Q2, a safety resistor F1 and at least one diode D1, wherein one end of the resistor R2 is connected to an output IO interface of the main control MCU circuit, the other end of the resistor R2 is connected in parallel with one end of the resistor R3 and a base of the transistor Q2, and the other end of the resistor R3 is connected in parallel with an emitter of the transistor Q2 and one end of the resistor R4 and then connected to a ground GND; the collector of the triode Q2 is connected with one end of the resistor R1, and the other end of the resistor R1 is connected with the base of the triode Q1; an emitting electrode of the triode Q1 is connected with one end of a safety resistor F1, and the other end of the safety resistor F1 is connected to a power input end VCCIN; the collector of the triode Q1 is connected with the other end of the resistor R4 and the anode of the diode D1 in parallel; the cathode of the diode D1 is connected in parallel with one end of the terminal resistor R5, and the cathode of the diode D1 is connected to the output interface of the differential bus high-end sending circuit.
4. The differential bus system as claimed in claim 3, wherein when the output IO interface of the main control MCU circuit outputs a low level, the voltage applied to the base of the transistor Q2 is a low level after being divided by the resistor R2 and the resistor R3, the transistor Q2 is turned off, the transistor Q2 is in an open circuit state, and the transistor Q1 is also in an open circuit state, the positive electrode of the diode D1 is at a zero level, the voltage of the output interface of the differential bus high-side transmitter circuit is in a quiescent state, and the voltage of the output interface of the differential bus high-side transmitter circuit is V _ OUT; when the output IO interface of the main control MCU circuit outputs high level, after voltage division is performed through the resistor R2 and the resistor R3, the voltage added to the base of the triode Q2 is high level, the base of the triode Q2 is in forward bias conduction, the collector level of the triode Q2 is equal to ground GND, the base of the triode Q1 is low level, the triode Q1 is in a conduction state, the collector voltage of the triode Q1 is equal to a power input end VCCIN, the diode D1 is in forward conduction because the power input end VCCIN is greater than V _ OUT, the forward voltage drop of the diode D1 is a constant value P, the cathode voltage of the diode D1 is VCCIN-P, and the voltage of the output interface in the high-end bus sending circuit is increased to VCCIN-P.
5. The differential bus system according to claim 4, wherein the differential bus low-side transmitting circuit comprises a resistor R6, a resistor R7, a transistor Q3 and at least one diode D2, wherein one end of the resistor R6 is connected to an output IO interface of the main control MCU circuit, and the other end of the resistor R6 is connected in parallel with one end of the resistor R7 and a base of the transistor Q3; the other end of the resistor R7 is connected with an emitting electrode of the triode Q3, and meanwhile, the other end of the resistor R7 is connected to a ground end GND in parallel; the collector of the triode Q3 is connected with one end of a resistor R9, and the collector of the triode Q3 is connected to the negative electrode of a diode D2 in parallel; the anode of the diode D2 is connected in parallel with the other end of the termination resistor R5, and the anode of the diode D2 is connected to the output interface of the low-side transmitting circuit of the differential bus.
6. The differential bus system according to claim 5, wherein when the output IO interface of the main control MCU circuit outputs a low level, the voltage applied to the base of the transistor Q3 is a low level after being divided by the resistors R6 and R7, at this time, the transistor Q3 is turned off, and the transistor Q3 is in an open circuit state, so that the cathode of the diode D2 is in an open circuit state, and since the levels of the output interfaces of the differential bus high-side transmitting circuit and the differential bus low-side transmitting circuit are kept equal in a static state by the adjustable differential bus circuit, the voltage of the output interface in the differential bus high-side transmitting circuit is V _ OUT; when the output IO interface of the main control MCU circuit outputs high level, after voltage division is performed through the resistor R6 and the resistor R7, the voltage added to the base electrode of the triode Q3 is high level, the forward bias of the triode Q3 is conducted at the moment, the voltage of the collector electrode of the triode Q3 is equal to the ground end GND, namely the voltage of the cathode electrode of the diode D2 is equal to the ground end GND, the forward voltage drop of the single diode D2 is a constant value P, so that the voltage is pulled down to P through the anode voltage of the diode D2, and the voltage of the output interface in the differential bus low-end sending circuit is pulled down to P.
7. The differential bus system of claim 6, wherein when the master MCU circuit is not transmitting data, the voltage of the output interfaces of the differential bus high-side transmitter circuit and the differential bus low-side transmitter circuit are both V _ OUT, and the voltage difference on the adjustable differential bus circuit is 0, and the voltage difference represents a binary number 0 in the data stream; when the master control MCU circuit transmits data, the voltage of the output interface of the low-end transmitting circuit of the differential bus is VCCIN-P, and the voltage of the output interface of the low-end transmitting circuit of the differential bus is P, so that the voltage difference V = VCCIN-2P between the voltage of the high-end differential bus and the voltage of the low-end differential bus, at the moment, the voltage difference V on the adjustable differential bus circuit represents binary number 1 in data stream, and the data transmission process from the output IO interface of the master control MCU circuit to the OBD diagnosis interface is realized through the voltage difference change of the adjustable differential bus circuit.
8. The differential bus system as claimed in claim 7, wherein the differential bus receiving circuit comprises a resistor R8, a resistor R9, a resistor R10, a resistor R11, a resistor R12 and a comparator U1A, wherein one end of the resistor R9 is connected to the cathode of the diode D2, and the other end of the resistor R9 is connected to the 2 nd pin of the comparator U1A; one end of the resistor R11 is connected to a power supply input end VCCIN, and the other end of the resistor R11 is connected with one end of the resistor R12 and the 3 rd pin of the comparator U1A in parallel; the other end of the resistor R12 is connected in parallel with a 4 th pin of the comparator U1A and then connected to a ground end GND, and an 8 th pin of the comparator U1A is connected to a power supply input end VCCIN; one end of the resistor R8 is connected with a power supply VCC3V3, the other end of the resistor R8 is connected with the 1 st pin of the comparator U1A and one end of the resistor R10 in parallel, and the other end of the resistor R10 is connected to an input IO interface of the master control MCU circuit.
9. The differential bus system according to claim 8, wherein when the binary data transmitted by the adjustable differential bus circuit is 1, the transistor Q3 in the low-side transmitting circuit of the differential bus is in a conducting state, and at this time, the voltage of the cathode of the diode D2 in the low-side transmitting circuit of the differential bus is P, and the voltage of the cathode of the diode D2 is loaded to the 2 nd pin of the comparator U1A through the resistor R9, and since the voltage of the 3 rd pin of the comparator U1A is greater than the voltage of the 2 nd pin of the comparator U1A, the 1 st pin of the comparator U1A outputs a high level and is connected to the input IO interface of the main control MCU circuit through the resistor R10, so that the input IO interface of the main control MCU circuit is a high level, and the input IO interface of the main control MCU circuit receives the binary data 1; when the binary data transmitted by the adjustable differential bus circuit is 0, the triode Q3 in the differential bus low-side transmitting circuit is in a cut-off state, at this time, the cathode voltage of the diode D2 of the differential bus low-side transmitting circuit is equal to the voltage V _ OUT of the output interface of the differential bus low-side transmitting circuit, the cathode voltage of the diode D2 is loaded to the 2 nd pin of the comparator U1A through the resistor R9, at this time, the 3 rd pin voltage of the comparator U1A is smaller than the 2 nd pin voltage of the comparator U1A, so that the 1 st pin of the comparator U1A outputs a low level and is connected to the input interface of the main control MCU circuit through the resistor IO 10, the input IO interface of the main control MCU circuit is a low level, and then the input IO interface of the main control MCU circuit receives the binary data 0.
10. The differential bus system as claimed in claim 8, wherein the resistance values of the resistors R11 and R12 are selected according to the formula R12 ÷ (R11 + R12) xvncin = V _ OUT/2, such that the voltage at pin 3 of the comparator U1A is equal to half the voltage at the output interface of the differential bus high-side transmitter circuit or the differential bus low-side transmitter circuit in the static state after the voltage is divided by the resistors R12 and R11.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211393569.XA CN115562249A (en) | 2022-11-08 | 2022-11-08 | Differential bus system for automobile diagnosis |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211393569.XA CN115562249A (en) | 2022-11-08 | 2022-11-08 | Differential bus system for automobile diagnosis |
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| CN115562249A true CN115562249A (en) | 2023-01-03 |
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| CN202211393569.XA Pending CN115562249A (en) | 2022-11-08 | 2022-11-08 | Differential bus system for automobile diagnosis |
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