CN216751748U

CN216751748U - Terminal resistor access control circuit, communication circuit and communication equipment

Info

Publication number: CN216751748U
Application number: CN202123272254.3U
Authority: CN
Inventors: 谭道海; 李显; 杨郑; 曹贤顺
Original assignee: Dongtu Science And Technology Yichang Co ltd
Current assignee: Dongtu Science And Technology Yichang Co ltd
Priority date: 2021-12-23
Filing date: 2021-12-23
Publication date: 2022-06-14
Anticipated expiration: 2031-12-23

Abstract

The application discloses a terminal resistor access control circuit, a communication circuit and a communication device. The terminal resistor access control circuit comprises: a first switching element, a second switching element, and a terminating resistor; the first switch element is connected with the second switch element and used for controlling the second switch element to switch the working mode; the second switch element is connected with the terminal resistor; the second switching element is used for connecting the termination resistor to the differential pair when in the first working mode, and is used for disconnecting the termination resistor from the differential pair when in the second working mode. When RS485 communication is carried out, the first switch element is operated to control the second switch element to switch the working mode, and the second switch element controls the terminal resistor, so that the terminal resistor can be conveniently and quickly connected to or disconnected from the differential pair, and the use flexibility is improved.

Description

Terminal resistor access control circuit, communication circuit and communication equipment

Technical Field

The application relates to the technical field of RS485 communication, in particular to a terminal resistor access control circuit, a communication circuit and communication equipment.

Background

The RS485 standard is a balanced transmission standard proposed by the american society for electronics industry. Because the data are transmitted by adopting differential signals, the remote communication capability of the RS485 standard is stronger.

When an RS485 network is constructed, because the input impedance of an RS485 transceiver is generally high, during long-distance and high-speed communication, when a signal is transmitted to the end of a bus, the instantaneous impedance may suddenly change, and signal reflection is caused, so that the communication quality is affected, for example, even if a signal conforming to a standard waveform is transmitted, data cannot be normally transmitted sometimes. In such scenarios, it is necessary to access the termination resistance at the end of the bus.

On the other hand, in the case of low-speed or short-distance communication, the signal reflection caused by the sudden change of the instantaneous impedance does not greatly affect the communication quality. However, access to the termination resistance increases power consumption and reduces on-load capability, e.g., the number of devices that can be connected on the bus decreases. In such scenarios, there is no need to access the termination resistance at the communication device.

Therefore, it is necessary to design the termination resistor access control circuit to enable easy selective access or disconnection of the termination resistor.

SUMMERY OF THE UTILITY MODEL

In view of the above problems of the prior art, the present application provides a termination resistance access control circuit, a communication circuit, and a communication device, which can conveniently select to access or disconnect a termination resistance when RS485 communication is performed.

In order to achieve the above object, a first aspect of the present application provides a termination resistor access control circuit, including: a first switching element, a second switching element, and a terminating resistor; the first switch element is connected with the second switch element and used for controlling the second switch element to switch the working mode; the second switch element is connected with the terminal resistor; the second switching element is used for connecting the termination resistor to the differential pair when in the first working mode, and is used for disconnecting the termination resistor from the differential pair when in the second working mode.

In the above, the terminating resistor is connected to the control circuit, and when the first switching element controls the second switching element to be in the first working mode, the second switching element enables the terminating resistor to be connected to the differential pair; when the first switch element controls the second switch element to be in the second working mode, the second switch element controls the terminal resistor to be disconnected with the differential pair. Therefore, the second switch element is controlled to switch the working mode by operating the first switch element, and the second switch element controls the terminal resistor, so that the terminal resistor is connected to or disconnected from the differential pair, and the operation is flexible, reliable and convenient.

In some embodiments, the second switching element comprises a triode; one end of the first switching element is connected with the base electrode of the triode, and the other end of the first switching element is grounded; the base electrode of the triode is also connected with a first direct current voltage through a first resistor.

Therefore, the first switch element is switched on or switched off, so that the base electrode of the triode is respectively connected with the ground or the first direct current voltage, and the voltage level of the base electrode of the triode is further changed to participate in controlling the conduction or the cut-off of the triode. When the voltage level of the base electrode of the triode is equal, the emitter electrode and the collector electrode of the triode are conducted; when the voltage level of the base electrode of the triode is equal, the emitting electrode and the collecting electrode of the triode are cut off. Therefore, the first switch element can flexibly, reliably and conveniently participate in controlling the conduction or the cut-off of the triode.

In some embodiments, the collector of the triode is grounded through the second resistor; and the emitter of the triode is connected with the second direct current voltage through a third resistor.

Therefore, the collector electrode of the triode is grounded through the second resistor, and the emitter electrode of the triode is connected with the second direct current voltage through the third resistor and respectively participates in controlling the conduction or the cut-off of the triode. Therefore, the triode can be flexibly, reliably and stably switched on or switched off.

In some embodiments, one end of the termination resistor is connected to the emitter of the transistor, and the other end of the termination resistor is connected to the third resistor; the other end of the terminal resistor is also used for being connected with a first communication line forming a differential pair; the second resistor is also used to connect with a second communication line forming a differential pair at one end near the collector of the transistor.

The termination resistor is connected to the emitter of the transistor, and is connected to the first communication line and the second communication line, which form the differential pair, via the emitter and the collector of the transistor, respectively. Controlled by the first switch element, when the base electrode of the triode is connected with the low level GND, the emitter electrode and the collector electrode of the triode are conducted, one end of the terminal resistor is connected with a first communication line JA (+) forming the differential pair, the other end of the terminal resistor is connected with a second communication line JB (-) forming the differential pair, and at this time, the terminal resistor is connected into the differential pair. Controlled by a first switching element, and connected to high level V at base of the triode_DD1When the switching element is turned off, the switching element is turned off between the emitter and the collector of the transistor, and one end of the termination resistor is disconnected from the first communication line JA (+) and the other end is disconnected from the second communication line JB (-) constituting the differential pair. Therefore, the termination resistor can be flexibly, reliably and conveniently connected to or disconnected from the differential pair.

In some embodiments, one end of the termination resistor is connected to the collector of the transistor, and the other end of the termination resistor is connected to the second resistor; the other end of the terminal resistor is also used for being connected with a second communication line forming a differential pair; the third resistor is also used for connecting with a first communication line forming a differential pair at one end close to the emitter of the triode.

In the above, the termination resistor is connected to the collector of the transistor, and the termination resistor is connected to the first communication line and the second communication line constituting the differential pair via the emitter and the collector of the transistor, respectively. Controlled by a first switching element, when the base of the triode is connected with a low level GND, the emitter and the collector of the triode are conducted, one end of a terminal resistor is connected with a first communication line JA (+) forming a differential pair, and the other end is connected with a second communication line JA forming a differential pairThe second communication line JB (-) of the pair is connected, and the termination resistor is connected to the differential pair. The base of the triode is connected with a high level V_DD1When the differential pair is formed, the emitter and the collector of the transistor are cut off, one end of the termination resistor is disconnected from the first communication line JA (+) forming the differential pair, and the other end is disconnected from the second communication line JB (-) forming the differential pair. Therefore, the termination resistor can be flexibly, reliably and conveniently connected to or disconnected from the differential pair.

In some embodiments, the first switching element comprises a manually operated switch.

Therefore, the manual operation switch can fix the body thereof on the shell of the communication equipment, and the operation part thereof is arranged outside the communication equipment, thereby facilitating the operation; and its pins are arranged on a printed circuit board inside the communication device. In this way, the manually operable switch can be operated flexibly, reliably and conveniently outside the housing of the communication device, and controls the second switching element, such as a transistor, and participates in controlling the connection or disconnection of the terminating resistor to or from the differential pair.

In some embodiments, the resistance of the termination resistor is adjustable within a predetermined range centered at 120 ohms.

Therefore, the resistance value of the terminal resistor can be adjusted, and the terminal resistor is adjusted within a preset range by taking the impedance characteristic of the shielded twisted pair as a center, namely 120 ohms, so as to realize a better impedance matching effect. Therefore, when the terminal resistor is connected to the differential pair, a better impedance matching effect can be realized, signal reflection is reduced, and communication quality is improved.

In some embodiments, the differential pair comprises a first communication line and a second communication line, the differential signal transmitted by the differential pair comprises a differential signal specified by the RS485 standard; the first communication line is at a positive level and the second communication line is at a negative level.

Thus, the first communication line and the second communication line constituting the differential pair transmit differential signals defined by the RS485 standard, and the first communication line is at a positive level and the second communication line is at a negative level. Therefore, when the terminal resistor is connected to differential time setting, a better impedance matching effect can be realized, signal reflection is reduced, and the communication quality of RS485 is improved. And when the communication device is idle, the first communication line is pulled up to a high level, the second communication line is pulled down to a low level, the differential pressure between the differential pairs is maintained in a stable state, and the communication quality of the RS485 is improved.

A second aspect of the present application provides a communication circuit comprising: the RS485 chip and the terminal resistor are connected into the control circuit; the two ends of the terminal resistor accessed to the control circuit are respectively connected with a first communication line and a second communication line which form a differential pair; and the first communication line and the second communication line which form the differential pair are respectively connected with the RS485 chip.

A third aspect of the present application provides a communication device, including: the RS485 chip, the control chip and the terminal resistor are connected into the control circuit; the two ends of the terminal resistor accessed to the control circuit are respectively connected with a first communication line and a second communication line which form a differential pair; a first communication line and a second communication line which form a differential pair are respectively connected with the RS485 chip; the control chip is connected with the RS485 chip to communicate through a first communication line and a second communication line which form a differential pair.

According to the terminal resistor access control circuit, the communication circuit and the communication equipment, when RS485 communication is carried out, the first switch element is utilized to control the second switch element to switch the working mode, the second switch element controls the terminal resistor to be selectively accessed into the communication line, the terminal resistor is conveniently and quickly accessed into or disconnected from the differential pair, and the flexibility in use is improved.

Drawings

The individual features and the connections between the individual features of the present application are further explained below with reference to the drawings. The figures are exemplary, some features are not shown to scale, and some of the figures may omit features that are conventional in the art to which the application relates and are not essential to the application, or show additional features that are not essential to the application, and the combination of features shown in the figures is not intended to limit the application. In addition, the same reference numerals are used throughout the specification to designate the same components. The specific drawings are illustrated as follows:

fig. 1 is a schematic diagram of a terminal resistor access control circuit according to an embodiment of the present application;

FIG. 2A is a schematic diagram of a communication circuit according to an embodiment of the present disclosure;

FIG. 2B is a schematic diagram of another communication circuit according to an embodiment of the present application;

fig. 3 is a schematic diagram of the components and external connections of the communication device according to the embodiment of the present application.

Detailed Description

The terms "first, second, third and the like" or "module a, module B, module C and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order, it being understood that specific orders or sequences may be interchanged where permissible to effect embodiments of the present application in other than those illustrated or described herein.

The term "comprising" as used in the specification and claims should not be construed as being limited to the contents listed thereafter; it does not exclude other elements or steps. It should therefore be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, and groups thereof. Thus, the expression "an apparatus comprising the devices a and B" should not be limited to an apparatus consisting of only the components a and B.

Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art from this disclosure.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. In the case of inconsistency, the meaning described in the present specification or the meaning derived from the content described in the present specification shall control. In addition, the terminology used herein is for the purpose of describing embodiments of the present application only and is not intended to be limiting of the present application.

To accurately describe the technical contents in the present application and to accurately understand the present application, the terms used in the present specification are given the following explanations or definitions before the description of the specific embodiments.

The Single-Chip Microcomputer or the Micro-controller (MCU) is an integrated circuit Chip, which is a small and perfect Microcomputer system formed by integrating the functions of a central processing Unit with data processing capability, a random access memory, a read only memory, various I/O ports, interrupt systems, a timer/counter and the like (possibly including a display driving circuit, a pulse width modulation circuit, an analog multiplexer, an a/D converter and the like) on a silicon Chip by adopting the super-large scale integrated circuit technology.

RS485 chip, which is an integrated circuit chip that transmits or receives data through a differential communication line, in a manner specified in the RS485 standard; the method can be used in RS485 communication equipment to form an RS485 transceiver.

A switching element, Switch, abbreviated SW.

The termination resistance access control circuit, the communication circuit, and the communication device according to the embodiment of the present application will be described in detail with reference to fig. 1 to 3.

First, an application scenario of the present application will be described.

The RS485 standard employs two communication lines, Ground (GND), which are typically differential communication. Typically, the RS485 differential pair is represented by the a line (or D +, high) and the B line (or D-, low). When the logic is '1', the voltage difference between the differential pairs is + (0.2-6) V, and when the logic is '0', the voltage difference between the differential pairs is- (0.2-6) V. Since RS485 is differential communication, the receiving data (for example, Rx is used as the identifier) and the transmitting data (for example, Tx is used as the identifier) cannot be performed simultaneously, so that the communication is half-duplex communication.

The RS485 standard adopts a combination of a balanced driver and a differential receiver, so that the anti-interference performance is obviously improved, for example, the farthest transmission distance can reach about 1200 meters. However, the transmission rate (hereinafter, rate) and the transmission distance (hereinafter, distance) are inversely proportional to each other when communication is performed using the RS485 standard, and the maximum transmission distance can be achieved only at a transmission rate of 100Kb/s or less.

In the case of long-distance, high-speed communication, when signals are transmitted to the end of the bus, reflections occur, thereby degrading the communication quality. In this case, it is necessary to connect an impedance matching resistor (hereinafter, referred to as a terminating resistor) to a communication device at the end of the bus. In the construction of an RS485 network, shielded twisted pair wires with impedance characteristics of 120 ohms (ohms, Ω) are typically used, and therefore, the termination resistor is typically selected to have a value comparable to the impedance characteristics of the cable, i.e., 120 ohms.

Currently, most of the terminating resistors are fixedly connected to the RS485 differential pair, for example, a position where the terminating resistor is connected to is reserved on a Printed Circuit Board (PCB), and whether the terminating resistor, such as a direct plug resistor or a chip resistor, is welded at the position is selected during later electrical installation. In this case, the termination resistor, once soldered, cannot be detached from the line in a non-destructive manner.

In other cases, however, access terminal resistance may cause communication instability. This is because, the larger the load on the RS485 bus, the lower the amplitude of the voltage output by the RS485 transceiver (provided with the RS485 chip), which in turn leads to deterioration of communication quality.

The terminal resistor access control circuit, the communication circuit and the communication equipment provided by the embodiment of the application provide a method for conveniently and rapidly accessing the terminal resistor, are flexible to operate and reliable to access, and enable the circuit or the equipment to be more flexible to use. For example, during field debugging, the working state of the terminal resistor can be flexibly set according to the actual use scene (such as transmission distance and transmission rate), so that the working efficiency of field debugging is improved, the use scene of the equipment is expanded, and the use efficiency of the equipment is improved. For example, when the termination resistor is disconnected (i.e., not connected) from the communication line, power consumption can be reduced, and the loaded capacity can be increased; when the termination resistor is accessed, signal reflection caused by impedance discontinuity can be reduced, and therefore communication quality is improved. For example, in the construction of an RS485 network, termination resistance access control circuitry is provided on the communication circuitry or communication device at the ends of the RS485 bus (e.g., the bus may have opposing ends) to control termination resistance access to the differential pair for long distance, and/or high rate communications and to control termination resistance disconnection from the differential pair for short distance, and/or low rate communications.

As shown in fig. 1, the termination resistor 30 of the embodiment of the present application accesses to the control circuit 1, and includes: a first switching element 10, a second switching element 20, and a terminating resistor 30; the first switch element 10 is connected with the second switch element 20, and the first switch element 10 is used for controlling the second switch element 20 to switch the working mode; the second switching element 20 is connected to the terminating resistor 30; the second switching element 20 is used to switch the terminating resistor 30 into the differential pair 40 when in the first mode of operation, and to switch the terminating resistor 30 out of the differential pair 40 when in the second mode of operation.

As described above, the terminating resistor 30 is connected to the control circuit, and when the first switching element 10 controls the second switching element 20 to be in the first operation mode, the second switching element 20 connects the terminating resistor 30 to the differential pair 40; when the first switching element 10 controls the second switching element 20 to be in the second operation mode, the second switching element 20 controls the terminating resistor 30 to be disconnected from the differential pair 40. Thus, the operation mode of the second switch element 20 is controlled by operating the first switch element 10, so that the termination resistor 30 is selectively connected to or disconnected from the differential pair 40, which is flexible, reliable and convenient.

Here, the first operation mode may be open or closed, may be on or off, and may be connected or disconnected; accordingly, the second mode of operation may be closed or open, may be off or on, and may be open or connected.

Here, the first switch element 10 or the second switch element 20 may be a manually operated key switch, a rotary switch, or a dial switch, and may be a remote or remotely operated electrical switch; the switching element may be a semiconductor element such as a transistor or a field effect transistor that performs a switching function by being turned on or off, an electrical element such as a relay that performs a switching function by being turned off or connected, or a manually operated switching element such as a pin or a jumper.

When the second switching element 20 includes a transistor, it may be a Field Effect Transistor (FET) or a transistor (transistor). When the transistor is used, it may be an NPN type tube (mostly silicon tube) or a PNP type tube (mostly germanium tube), where N is a Negative electrode (Negative) and P is a Positive electrode (Positive). The polarity of the power supplies of the NPN type tube and the PNP type tube are different, but the working principle is the same. For example, a circuit using a PNP type transistor can be equivalently obtained from a circuit composition using a NPN type transistor, or a circuit using a PNP type transistor can be equivalently obtained from a circuit composition using a NPN type transistor. When the PNP type tube is used, the polarity of the DC power supply when the NPN type tube is used is reversed. The following examples are described with reference to PNP transistors.

When the base electrode of the PNP type triode is at low level, the emitter electrode is conducted with the collector electrode, and current flows through the emitter electrode and the collector electrode. When the base electrode of the PNP type triode is at high level, the emitting electrode and the collecting electrode are cut off, and no current flows through.

In some embodiments, as shown in fig. 2A and 2B, the termination resistor is connected to the control circuit, and the second switching element includes a transistor Q3; one end of the first switching element SW1 is connected to the Base (Base) of the transistor Q3, and the other end of the first switching element SW1 is grounded to GND; the base of the triode Q3 is also connected with a first direct current voltage V through a first resistor R10_DD1And (4) connecting.

Here, the first DC voltage V_DD1The voltage level of (a) is determined by each component, and may be 3.3V or 5V.

As shown in fig. 2A and 2B, the terminal resistor is connected to the control circuit, and when the first switch element SW1 is closed (On), the first dc voltage V is obtained_DD1The circuit to ground GND is completed and current flows through a first resistor R10, which is close to one of transistor Q3The voltage level of the terminal is ground GND, i.e. the base of the transistor Q3 is connected to low level. At this time, the transistor Q3 is in a conducting state; when the first switching element SW1 is Off (Off), the first dc voltage V_DD1The circuit between the ground GND and the ground GND is broken, no current flows through the first resistor R10, and the voltage level of the first resistor close to one end of the triode Q3 is the first direct-current voltage V_DD1I.e., the base of transistor Q3 is tied high. At this time, the transistor Q3 is in the off state.

In this way, the base of the transistor Q3 can be connected to ground or the first dc voltage via the on/off of the first switching element SW1, so as to change the voltage level of the base of the transistor Q3, thereby participating in controlling the on/off of the transistor Q3. Therefore, the first switch element can flexibly, reliably and conveniently participate in controlling the conduction or the cut-off of the triode.

In some embodiments, as shown in fig. 2A and 2B, the termination resistor is connected to the control circuit, and the Collector (Collector) of the transistor Q3 is connected to GND through the second resistor R20; an Emitter (Emitter) of the transistor Q3 is connected to the second DC voltage V via a third resistor R30_DD2And (4) connecting.

Here, the second resistor R20 is a pull-down resistor, and its resistance value is selected according to the transistor Q3; either a fixed resistance or an adjustable resistance. The third resistor R30 is a pull-up resistor, and the resistance value of the third resistor R30 is selected according to the triode Q3; either a fixed resistance or an adjustable resistance.

Here, the second DC voltage V_DD2The voltage level of the voltage is determined according to each component and can be 3.3V or 5V; can be matched with the first direct current voltage V_DD1Are the same or different.

As shown in fig. 2A and 2B, the termination resistor is connected to the control circuit, the collector of the transistor Q3 is grounded through the second resistor, and the emitter of the transistor Q3 is connected to the second dc voltage through the third resistor, so as to implement bias conditions of the collector and the emitter respectively, and participate in controlling the conduction or the cut-off of the transistor together. Thus, the transistor Q3 is controlled by the first switch element SW1, and can be flexibly, reliably and stably turned on or off.

In some embodiments, as shown in fig. 2A, one end of termination resistor R100 is connected to the emitter of transistor Q3; the other end of the termination resistor R100 is connected to the third resistor R30, and the other end of the termination resistor R100 is also used for connection to a first communication line JA (+) constituting the differential pair 40; the second resistor R20 is also connected to a second communication line JB (-) forming the differential pair 40 at one end near the collector of the transistor Q3.

As shown in fig. 2A, the terminating resistor R100 is connected to the emitter of the transistor Q3, and is connected to the first communication line and the second communication line constituting the differential pair via the emitter and the collector of the transistor, respectively. When the base of the transistor Q3 is connected to the low level GND by the first switching element SW1, the emitter and the collector of the transistor Q3 are turned on, one end of the terminal resistor R100 is connected to the first communication line JA (+) constituting the differential pair, and the other end is connected to the second communication line JB (-) constituting the differential pair, and at this time, the terminal resistor R100 is connected to the differential pair. Controlled by a first switching element SW1, a high level V is connected to the base of a triode Q3_DD1When the transistor Q3 is turned off between the emitter and the collector, one end of the terminating resistor R100 is disconnected from the first communication line JA (+) constituting the differential pair, and the other end is disconnected from the second communication line JB (-) constituting the differential pair, and the terminating resistor R100 is disconnected from the differential pair. Therefore, the termination resistor can be flexibly, reliably and conveniently connected to or disconnected from the differential pair.

In some embodiments, as shown in fig. 2B, one end of the termination resistor R100 is connected to the collector of the transistor Q3, and the other end of the termination resistor R100 is connected to the second resistor R20; the other end of the termination resistor R100 is also used for connection to a second communication line JB (-) forming a differential pair; the third resistor R30 is also connected to a first communication line JA (+) at a terminal near the emitter of the transistor Q3.

As shown in fig. 2B, a termination resistor R100 is connected to the collector of the transistor Q3, and the termination resistor is connected to the first communication line and the second communication line constituting the differential pair via the emitter and the collector of the transistor, respectively. Controlled by a first switching element SW1, when the base of a triode Q3 is connected with a low level GNDWhen the emitter and the collector of Q3 are turned on, one end of the termination resistor R100 is connected to the first communication line JA (+) constituting the differential pair, and the other end is connected to the second communication line JB (-) constituting the differential pair, the termination resistor R100 is connected to the differential pair. The base of the triode Q3 is connected with a high level V_DD1When the transistor Q3 is turned off between the emitter and the collector, one end of the termination resistor R100 is disconnected from the first communication line JA (+) constituting the differential pair, and the other end is disconnected from the second communication line JB (-) constituting the differential pair, the termination resistor R100 is disconnected from the differential pair. Therefore, the termination resistor can be flexibly, reliably and conveniently connected to or disconnected from the differential pair.

As shown in fig. 2A and 2B, in the communication circuit 2A or 2B, when the communication circuit is idle (no RS485 communication), the first communication line JA (+) is pulled up to a high level by the third resistor, and the second communication line JB (-) is pulled down to a low level by the second resistor, and the differential voltage between the differential pair is maintained in a stable state, whereby the communication quality and reliability of the RS485 can be improved.

In some embodiments, the first switching element comprises a manually operated switch. As shown in fig. 3, the body 70 of the manually-operated switch is fixed to the housing 80 of the communication device 200; the operation part 90 is arranged outside the communication equipment 200, so that the operation without opening the box is convenient; its pin JP4 is provided on the PCB board 400 inside the communication device 200. In this way, the manually operated switch can be flexibly, reliably and conveniently operated outside the housing of the communication device to control the on/off of the transistor Q3, so that the termination resistor R100 is connected to or disconnected from the differential pair.

The manual operation switch may be a key switch, a dial switch, a knob switch, or the like.

In some embodiments, the resistance of the termination resistor is adjustable within a predetermined range centered at 120 ohms, such as a range of 110 ohms to 130 ohms.

Therefore, the terminal resistor with the adjustable resistance value is selected, the impedance characteristic of the shielded twisted-pair is centered on 120 ohms, and the impedance matching effect can be better achieved within a preset range. Therefore, when the terminal resistor is connected to the differential pair, a better impedance matching effect can be realized, signal reflection is reduced, and communication quality is improved.

In some embodiments, as shown in fig. 3 and fig. 2A and 2B, the differential signal transmitted by the first communication line JA (+) and the second communication line JB (-) constituting the differential pair includes a differential signal specified by the RS485 standard, the first communication line is at a positive level, and the second communication line is at a negative level.

Thus, the first communication line and the second communication line constituting the differential pair transmit differential signals defined by the RS485 standard. Therefore, when the terminal resistor is connected to differential time setting, a better impedance matching effect can be realized, signal reflection is reduced, and the communication quality of RS485 is improved.

The terminal resistor access control circuit provides a method for conveniently and quickly accessing the terminal resistor into the RS485 communication circuit, and is flexible in operation, reliable in access and more flexible in use. For example, when the terminal resistor is not connected, the power consumption can be reduced, and the capacity with load can be increased; when the termination resistor is accessed, signal reflection caused by impedance discontinuity can be reduced, and therefore communication quality is improved. The terminal resistor access control circuit can be used in a communication circuit to realize one-to-one communication of two RS485 communication devices; the method can also be used in a communication circuit to realize networking communication of a plurality of RS485 communication devices in a bus mode.

As shown in fig. 2A and 2B, the communication circuit 2A or 2B according to the embodiment of the present invention includes an RS485 chip 50 and the terminal resistor access control circuit, both ends of the terminal resistor access control circuit are connected to a first communication line JA (+) and a second communication line JB (-) that form a differential pair, respectively, and the first communication line JA (+) and the second communication line JB (-) that form the differential pair are connected to the RS485 chip, respectively.

In the above, after the communication circuit is provided with the terminal resistor access control circuit, the terminal resistor can be controlled to be accessed into or disconnected from the differential pair on the communication circuit or the communication equipment located at the starting end node or the end node of the RS485 bus; or on a communication circuit or communication device located on other nodes of the RS485 bus, the termination resistors can be controlled to disconnect from the differential pairs. Therefore, the communication circuit or the communication equipment of the same type can be used on different nodes of the RS485 bus, and the flexibility, the replaceability and the convenience of deployment are enhanced.

Therefore, when the communication is carried out at a long distance and a high speed, the terminal resistor is connected to the differential pair so as to improve the communication quality; in short-range, low-speed communication, the termination resistor is disconnected from the differential pair to reduce power consumption and increase load capacity. In the above way, the communication circuit provides a method for conveniently and rapidly accessing the terminal resistor, and has the advantages of flexible operation, reliable access and more flexible use.

As shown in fig. 3, the communication device 200 according to the embodiment of the present application further includes: the RS485 chip 50, the control chip 60 and the terminal resistor are connected into the control circuit; both ends of a terminal resistor R100 of the terminal resistor access control circuit are respectively connected with a first communication line JA (+) and a second communication line JB (-) which form a differential pair; a first communication line JA (+) and a second communication line JB (-) which constitute a differential pair are connected to the RS485 chip 50, respectively; the control chip 60 is connected to the RS485 chip 50 to communicate through a first communication line JA (+) and a second communication line JB (-) constituting a differential pair.

As shown in fig. 3, the communication device 200 communicates with other communication devices (not shown) via its connected shielded twisted pair 300 in RS485 protocol.

Above, the control chip 60 may be a single chip or a microcontroller, and is configured to generate data to be sent via the RS485 protocol or receive data via the RS485 protocol. The generated data is sent to other RS485 communication equipment through the RS485 chip 50; or receive the data sent by other RS485 communication devices via the RS485 protocol via the RS485 chip 50. Since the RS485 protocol is in a half-duplex operating mode, a control port for controlling switching between receiving and transmitting is usually provided between the RS485 chip 50 and the control chip 60, in addition to two Input/Output (IO) ports, i.e. receiving (Rx) and transmitting (Tx), for example, a program code running on the control chip 60 adjusts a signal for the control port, so as to control or switch receiving or transmitting of the RS485 chip 50.

As shown in fig. 3, the communication device 200 may further include: a housing 80, an operation switch (a reference thereof is not provided), a transistor Q3, and a terminating resistor R100; at least one printed circuit board 100 is disposed within the housing; an operating switch, which comprises a body 70, an operating part 90 and a pin JP4, wherein the operating part 90 is arranged on the body 70, the pin JP4 is connected to the body through a connecting wire, and the operating part is electrically connected with the pin by the body 70; an operation hole is formed on the outer wall of the casing 80, and the body 70 of the operation switch is arranged on the casing through the operation hole; the pin JP4 of the operation switch is disposed on a printed circuit board, the transistor Q3 is disposed on a printed circuit board, and the terminal resistor R100 is disposed on a printed circuit board. Above, each component can be arranged on the same printed circuit board, and can also be arranged on different printed circuit boards, and the components are connected in the manner described above, and are not described again.

In some embodiments, an RS485 connector can be further included, and the RS485 connector includes an external connection part and a pin part; an RS485 hole is formed in the outer wall of the shell, and an external connection part of the RS485 connector penetrates through the RS485 hole and is arranged on the shell; the pin part of the RS485 connector is arranged on a printed circuit board.

As shown in fig. 3, the RS485 chip 50 is disposed on a printed circuit board; the control chip 60 is disposed on a printed circuit board.

As shown in fig. 2A, 2B, and 3, in response to the closing (On) operation of the operating unit 90, the transistor Q3 is turned On, and the terminating resistor R100 is connected to the first communication line JA (+) and the second communication line JB (-) led out from the pin portion of the RS485 connector; in response to an Off operation of the operating unit 90, the transistor is turned Off, and the terminal resistor is disconnected from the first communication line JA (+) and the second communication line JB (-) drawn from the pin portion of the RS485 connector.

The control logic that the terminal resistor is connected when the operating part 90 is closed and the terminal resistor is disconnected when the operating part is opened accords with the ergonomic design, so that the operation reliability is high, and the accidents caused by misoperation can be reduced.

Therefore, the manual operation switch is adopted to control the conduction or the cut-off of the triode Q3 (such as working in a cut-off region or a saturation region), and the conduction or the cut-off of the triode Q3 is utilized to control the connection or the disconnection of the terminal resistor, so that the device is reliable, flexible, safe and convenient, and the cost can be reduced.

In some embodiments, as shown in fig. 2A, 2B and 3, the manually operated switch is a dip switch. A dial switch, also called a dip switch, is a micro switch that needs manual operation, and generally includes a body, an operation button, and a package portion. The dial can be conveniently arranged outside the communication equipment, for example, the body of the dial is fixedly arranged in a hole formed in the outer wall of the shell, and the dial is displayed outside the communication equipment. Generally, each dial of the dial switch has two pins, which are connected to a package portion disposed on the PCB board through wires. The DIP Switch is usually In a Package form of a standard Dual In-line Package (DIP), and is disposed on a PCB board In a Surface Mount Technology (SMT) manner, so that the DIP Switch is also called a DIP Switch (DIP Switch), and a position where a pin is disposed on the PCB is a connection Point (JP). The dial of the dial switch is toggled to an On position, so that the switch is closed, two pins of the switch are connected through a connection point JP, and then the dial switch is kept normally closed and is in a closed state; conversely, the dial of the dial switch is toggled to the Off position, so that the switch is turned Off, the two pins of the switch are turned Off by the connection point JP, and then the dial switch is kept normally Off and is in the Off state.

To achieve impedance matching with the RS485 chip as accurately as possible, the termination resistor is typically placed as close to the RS485 chip 50 as possible. In this case, as shown in fig. 3, the transistor Q3 can electrically and reliably separate the pin JP4 of the operation switch, the body 70, the terminal resistor R100, and the differential pair, and the routing manner of the control line from the pin of the operation switch to the body of the operation switch and the length of the accumulated control line, or the routing manner of the control line from the transistor Q3 to the terminal resistor R100 and the length of the accumulated control line, or the routing manner of the control line from the pin of the operation switch to the transistor Q3 and the length of the accumulated control line can be easily adjusted according to the need of wiring, so that the occurrence of signal reflection due to impedance discontinuity can be effectively avoided, and the transmission quality of signals on the communication line can be prevented from being affected.

On the other hand, the transistor Q3 electrically and reliably separates the pin JP4 of the operation switch, the body 70, the terminal resistor R100, and the differential pair, and can avoid the antenna effect that may exist in the control line from the differential pair or the terminal resistor to the transistor Q3, or the control line from the transistor Q3 to the pin JP4 of the operation switch, the body 70, and the operation unit 90 when the operation switch is not closed, and therefore, the communication quality can be further improved.

As described above, the transistor Q3 electrically and reliably separates the terminal resistor R100 from the terminal pin JP4 and the body 70 of the operation switch, so that the terminal resistor R100 and the terminal pin JP4 of the operation switch can be located at a relatively long distance, and the terminal resistor R100, the terminal pin JP4, or the transistor Q3 can be flexibly arranged on the PCB, respectively, thereby preventing the communication quality from being degraded due to the fact that the terminal resistor is located far from the RS485 chip because of the limitation that the two terminals must be located nearby. For example, the pin JP4 of the operation switch is disposed near the edge of the PCB to minimize the length of the connection line between the body and the pin. For example, the terminal resistor R100 is placed as close to the RS485 chip 50 as possible, the cumulative length of the control line between the terminal resistor R100 and the RS485 chip 50 is L2 (illustrated by a straight line distance in the figure, and may be a connection line composed of multiple broken lines in a specific implementation), and the cumulative length of the control line between the terminal resistor R100 and the pin JP4 of the operation switch is L1 (illustrated by a straight line distance in the figure, and may be a connection line composed of multiple broken lines in a specific implementation), so that L1 is not smaller than L2, thereby improving the quality of the wiring.

So, triode Q3's switch and isolation for there is not the dependency in the position terminal resistance and dial switch, can set up terminal resistance or dial switch's pin on the PCB board according to the wiring condition of reality in a flexible way, optimize the overall arrangement of components and parts on the PCB board, control is reliable, accords with the electromagnetic interference design standard, can maximize RS485 differential transmission's advantage.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. In the case of inconsistency, the meaning described in the present specification or the meaning derived from the content described in the present specification shall control. In addition, the terminology used herein is intended to describe embodiments of the application

Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the technical solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

It can be clearly understood by those skilled in the art that, for convenience and simplicity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.

Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art from this disclosure. It should be noted that the foregoing is only illustrative of the preferred embodiments of the present application and the technical principles employed. It will be understood by those skilled in the art that the present application is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the application. Therefore, although the present application has been described in more detail with reference to the above embodiments, the present application is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present application.

Claims

1. A termination resistance access control circuit, comprising:

a first switching element, a second switching element, and a terminating resistor;

the first switch element is connected with the second switch element and used for controlling the second switch element to switch the working mode;

the second switch element is connected with the terminal resistor;

the second switch element is used for connecting the terminal resistor into the differential pair when in the first working mode,

the second switching element is used for disconnecting the termination resistor from the differential pair when in the second operating mode.

2. The control circuit of claim 1,

the second switching element comprises a triode;

one end of the first switching element is connected with the base electrode of the triode, and the other end of the first switching element is grounded;

the base electrode of the triode is also connected with a first direct current voltage through a first resistor.

3. The control circuit of claim 2,

the collector of the triode is grounded through a second resistor;

and the emitter of the triode is connected with the second direct current voltage through a third resistor.

4. The control circuit of claim 3,

one end of the terminal resistor is connected with the emitting electrode of the triode,

the other end of the terminal resistor is connected with the third resistor;

the other end of the terminal resistor is also used for being connected with a first communication line forming a differential pair;

and one end of the second resistor close to the collector of the triode is also used for being connected with a second communication line forming a differential pair.

5. The control circuit of claim 3,

one end of the termination resistor is connected with the collector of the triode,

the other end of the terminal resistor is connected with the second resistor;

the other end of the terminal resistor is also used for being connected with a second communication line forming a differential pair;

and the third resistor is also used for being connected with a first communication line forming a differential pair at one end close to the emitter of the triode.

6. The control circuit of claim 1,

the first switching element comprises a manually operated switch.

7. The control circuit of claim 1,

the resistance value of the terminal resistor is adjustable within a preset range with 120 ohms as the center.

8. The control circuit of any one of claims 1 to 7,

the differential pair comprises a first communication line and a second communication line, and differential signals transmitted by the differential pair comprise differential signals specified by RS485 standard;

the first communication line is at a positive level and the second communication line is at a negative level.

9. A communication circuit, comprising:

an RS485 chip, the terminal resistor access control circuit of any one of claims 1 to 7;

the two ends of the terminal resistor access control circuit are respectively connected with a first communication line and a second communication line which form a differential pair;

and the first communication line and the second communication line which form the differential pair are respectively connected with the RS485 chip.

10. A communication device, comprising:

the RS485 chip, the control chip and the terminal resistor access control circuit of any one of claims 1 to 7;

the first communication line and the second communication line which form the differential pair are respectively connected with the RS485 chip;

the control chip is connected with the RS485 chip to communicate through the first communication line and the second communication line which form the differential pair.