CN101572642A - RS485 communication circuit - Google Patents
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- CN101572642A CN101572642A CNA2009100868916A CN200910086891A CN101572642A CN 101572642 A CN101572642 A CN 101572642A CN A2009100868916 A CNA2009100868916 A CN A2009100868916A CN 200910086891 A CN200910086891 A CN 200910086891A CN 101572642 A CN101572642 A CN 101572642A
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Abstract
The invention relates to a RS485 communication circuit which can be used for enhancing the anti-interference capability and drive capability of RS485 communication and uses a sending signal to indirectly control the receiving/sending direction to lead a main control chip not to independently process the control of data stream direction. The circuit comprises a power supply isolation module (10), the main control chip (20), a signal photoelectric isolation module (30) and a communication interface module (40); wherein, the power supply isolation module (10) generate 5V isolating power source which is used for supplying power for the communication interface module; the signal photoelectric isolation module (30) includes a data receiving signal optical isolation circuit (31) and a data sending signal optical isolation circuit (32), wherein, the data receiving signal optical isolation circuit (31) is respectively connected with the main control chip (20) and the communication interface module (40), and the data sending signal optical isolation circuit (32) is respectively connected with the main control chip (20) and the communication interface module (40); the communication interface module (40) comprises a receiving signal shaping drive circuit (41), a data sending control circuit (42), a RS485 communication interface chip (43) and a bus interface circuit (44).
Description
Technical field
The present invention relates to a kind of RS485 communicating circuit, in particular, relate to a kind of RS485 communicating circuit that is applied to the intelligent automation device in industrial automation monitoring field.
Background technology
Usually, in the industrial automation field, in the transformer and distribution power station supervisory control system, the terminal data collection block adopts the distributed capture mode usually, and measured data such as voltage, electric current, power etc. generally are connected to background monitoring system by fieldbus.Current fieldbus kind is more, as RS485 bus, CAN bus, Profibus bus, DeviceNet bus, Longworks bus or the like.Wherein because characteristics such as low, the easy realizations of RS485 bus hardware cost, good reliability, so it is widely used in the intelligent automation device in the industrial automation monitoring field.
The RS485 bus is a half-duplex bus, use in industry spot, general communication speed is under 19.2kpbs, and bus transfer is 1200 meters apart from theoretical value, but, actually can transmit hundreds of meters even lower because the capacity of influence of the electromagnetic environment of industry spot and bus node limits.
Generally speaking, for realizing the RS485 communication, on hardware circuit, need main control chip (CPU) and RS485 communication interface chip at least.Main control chip can be 8 single-chip microcomputers of 51 kernels, 16 single-chip microcomputers of risc architecture, ARM kernel 16 or 32 single-chip microcomputers or the like; The RS485 communication interface chip can adopt SN75176, Max485,65LBC184 or the like.As shown in Figure 1, general, main control chip (CPU) needs to use three holding wires to be connected with communication interface chip, the data-signal receiving terminal (RXD) that these three holding wires are respectively main control chips, data-signal transmitting terminal (TXD), Data Receiving/transmission control end (Control), be connected with the RS485 communication interface chip respectively, wherein the holding wire of data-signal receiving terminal (RXD) and data-signal transmitting terminal (TXD) generally uses the lead-in wire of the asynchronous serial communication mouth of main control chip (CPU), and Data Receiving/transmission control end generally uses the common IO mouth of main control chip (CPU) to get final product.These three holding wires are connected with the RS485 communication interface chip, wherein data-signal receiving terminal (RXD) is connected with the data output end (R) of RS485 communication interface chip, data flow is (CPU) from the RS485 communication interface chip to main control chip, shown in the arrow among Fig. 1, show that bus data that the RS485 communication chip receives is transferred to the data-signal receiving terminal (RXD) of main control chip (CPU) from the data output end (R) of RS485 communication interface chip; Data-signal transmitting terminal (TXD) is connected with the data input pin (D) of RS485 communication interface chip, data flow is to the RS485 communication interface chip from main control chip (CPU), shown in the arrow among Fig. 1, show that the data of main control chip (CPU) transmission are transferred to the data input pin (D) of RS485 communication interface chip by signal sending end (TXD) lead-in wire; The Data Receiving of main control chip (CPU)/transmission control end (Control) links to each other with the Data Receiving/transmission Enable Pin (RE/DE) of RS485 communication interface chip, data flow is to the RS485 communication interface chip, shown in the arrow among Fig. 1 from main control chip (CPU).Under current background technology, isolate needs if consider electromagnetic compatibility (EMC) performance of device and communication, can also carry out the photoelectricity isolation processing respectively to three holding wires of above-mentioned main control chip (CPU), make communication interface part and main control part realize electrical isolation.
The weak point of technology existence at present is: at first, because device is applied to industrial occasions, there is a large amount of electromagnetic interference signals around the device, comprise the interference signal that some are introduced from the RS485 bus, install the interference of internal circuit in addition, make the bus communication ability actual performance of RS485 reduce, as the quantity minimizing of connected node on communication distance shortening, the bus.Secondly, main control chip and communication interface chip need three holding wires and are connected and realize the RS485 communication, wherein reception/sending direction control line (Control) needs main control chip (CPU) to carry out program control according to the current direction of data flow, and is relatively loaded down with trivial details.
Summary of the invention
At the deficiencies in the prior art, the invention provides a kind of RS485 communicating circuit, it can strengthen the antijamming capability and the driving force of RS485 communication, and uses transmission signal (TXD) control reception/sending direction indirectly, makes main control chip (CPU) need not the control of individual processing data flow direction.
RS485 communicating circuit of the present invention comprises main control chip (CPU), power isolation module, signal photoelectric isolation module and communication interface module;
Described power isolation module produces the 5V insulating power supply, is used for communication interface module is powered, and makes communication interface module and main control chip (CPU) carry out isolated from power;
Described signal photoelectric isolation module comprises that data reception signal optically coupled isolation circuit and data send the flashlight buffer circuit.The data reception signal optically coupled isolation circuit is connected with communication interface module with described main control chip (CPU) respectively, be used for the data that communication interface module is received from the RS485 bus interface are isolated, and data-signal receiving terminal (RXD) the data transmission flashlight buffer circuit that is sent to main control chip (CPU) is connected with communication interface module with described main control chip (CPU) respectively, be used for the transmission signal of the data-signal transmitting terminal (TXD) of main control chip (CPU) is isolated, and be transferred to communication interface module.
Described communication interface module is made up of received signal plastic drive circuit, data sending controling circuit, RS485 communication interface chip and bus interface circuit.The input of received signal plastic drive circuit is connected with the data output end (R) of described RS485 communication interface chip, the output of received signal plastic drive circuit is connected with described data reception signal optically coupled isolation circuit, output signal to the data output end of RS485 communication interface chip is carried out waveform shaping, thereby improves its driving force; The input of data sending controling circuit sends the flashlight buffer circuit with described data and is connected, the output of data sending controling circuit is connected with the Data Receiving/transmission Enable Pin (RE/DE) and the data input pin (D) of described RS485 communication interface chip respectively, realizes the transmission to the RS485 communication interface chip of the automatic control of described RS485 communication interface chip reception/sending direction and data; Described RS485 communication interface chip is common communication interface chip, as: MAX485 of the SN75176 of TI company, 65LBC184 or U.S. letter company or the like; The input of described bus interface circuit is connected with the bus difference output end (A, B) of described RS485 communication interface chip, and the output of bus interface circuit is connected with on-the-spot RS485 bus.
Description of drawings
Fig. 1 is the block diagram of RS485 communication in the prior art;
Fig. 2 is the structured flowchart of one embodiment of the invention;
Fig. 3 (A) is the circuit diagram that data reception signal photoelectricity is isolated;
Fig. 3 (B) is that data send the circuit diagram that signal photoelectricity is isolated;
Fig. 4 is the circuit diagram of received signal plastic drive circuit;
Fig. 5 is the oscillogram of input of received signal plastic drive circuit comparator and output;
Fig. 6 is the circuit diagram of data sending controling circuit;
Fig. 7 is the circuit diagram of bus interface circuit.
Embodiment
Figure 2 shows that the structured flowchart of RS485 communicating circuit in a preferred embodiment of the invention, this RS485 communicating circuit comprises power isolation module 10, main control chip 20, signal photoelectric isolation module 30 and communication interface module 40.
Signal photoelectric isolation module 30 comprises data reception signal optically coupled isolation circuit 31 and data send flashlight buffer circuit 32, data reception signal optically coupled isolation circuit 31 is connected with the RXD pin of main control chip 20, and data send flashlight buffer circuit 32 and are connected with the TXD pin of main control chip 20.
Fig. 3 (A) is the circuit diagram that data reception signal photoelectricity is isolated; Fig. 3 (B) is that data send the circuit diagram that signal photoelectricity is isolated.Shown in Fig. 3 (A), received signal optically coupled isolation circuit 31 comprises the first pull-up resistor R11, the first current-limiting resistance R12 and the first optocoupler U1, be connected to the input of the first optocoupler U1 from the signal of plastic drive circuit 41 in the communication interface module 40 through the first current-limiting resistance R12, the output of the first optocoupler U1 is connected to the RXD pin of main control chip 20 through the first pull-up resistor R11.Shown in Fig. 3 (B), send flashlight buffer circuit 32 and comprise the second pull-up resistor R21, the second current-limiting resistance R22 and the second optocoupler U2, be connected to the input of the second optocoupler U2 from the signal of main control chip 20 pin TXD through the second current-limiting resistance R22, the output of the second optocoupler U2 is connected to the data sending controling circuit 42 of communication interface module 40 through the second pull-up resistor R21.Among this embodiment, optocoupler adopts the TLP521-1 chip of Toshiba, and the optocoupler of other types also can use, especially under the situation of communication speed greater than 9.6kbps, should use the high speed photo coupling chip, as the 6N137 of Toshiba, the HCPL-0611 of Agilent company etc.
Fig. 4 is the circuit theory diagrams of the received signal plastic drive circuit 41 of communication interface module 40, and this circuit comprises the first divider resistance R30, the second divider resistance R31, the 3rd pull-up resistor R32, the 4th pull-up resistor R33 and the first voltage comparator U4A.The output signal of communication interface chip 43 is exported by the R pin, after drawing on the 3rd pull-up resistor R32, insert the positive input terminal of the first voltage comparator U4A, the 3rd pull-up resistor R32 is connected between power supply VCC2 and the R pin, the first divider resistance R30 and the second divider resistance R31 are series between power supply VCC2 and the ground GND2, and the tie point between the first divider resistance R30 and the second divider resistance R31 is received the negative input end of the first voltage comparator U4A, and power supply VCC2 and ground GND2 are the 5V power supplys through isolating.The output of the first voltage comparator U4A is connected to data reception signal optically coupled isolation circuit 31, the four pull-up resistor R33 and is connected between the output of the power supply VCC2 and the first voltage comparator U4A through after drawing on the 4th pull-up resistor R33.The level of the negative input end of the first voltage comparator U4A is to be formed after to power supply VCC2 dividing potential drop by the first divider resistance R30 and the second divider resistance R31, is generally about 2V.When the positive input terminal voltage of the first voltage comparator U4A during greater than 2V, the output level of the first voltage comparator U4A is a high level, when the positive input terminal voltage of the first voltage comparator U4A during less than 2V, the level of the output of the first voltage comparator U4A is a low level, and Fig. 5 has described negative input end, the positive input terminal of the first voltage comparator U4A, the waveform corresponding diagram of output.By plastic drive circuit 41, will come from the signal that communication interface chip signal output R pin distorted and carry out shaping, and for received signal optically coupled isolation circuit 31 provides the driving of signal, thereby strengthen the antijamming capability and the driving force of RS485 communication.
Fig. 6 is the circuit theory diagrams of the data sending controling circuit 42 of communication interface module 40, this circuit comprises the 3rd divider resistance R40, the 4th divider resistance R41, the 5th pull-up resistor R42 and the second voltage comparator U4B, the 3rd divider resistance R40 and the 4th divider resistance R41 are connected between power supply VCC2 and the ground GND2, and the 5th pull-up resistor (R42) is connected between the power supply VCC2 and the second voltage comparator U4B output; Wherein the first divider resistance R30 and the second divider resistance R31 in the 3rd divider resistance R40 and the 4th divider resistance R41 and the plastic drive circuit 41 can carry out multiplexing.The signal that sends flashlight buffer circuit 32 from data is input to the negative input end of the second voltage comparator U4B, also is input to the D pin of communication interface chip 43 simultaneously.Be input to the positive input terminal of the second voltage comparator U4B through the fixed level (being generally about 2V) of the 3rd divider resistance R40 and the formation of the 4th divider resistance R41 dividing potential drop.The output of the second voltage comparator U4B is connected to the RE/DE end of communication interface chip 43.When the level of U4B negative input end during greater than 2V, U4B is output as low level, otherwise when the level of U4B negative input end during less than 2V, U4B is output as high level, this circuit has played inverting function, is used to control the Data Receiving of communication interface chip 43 or the direction selection of transmission.By data sending controling circuit 42, use to send signal (TXD) control reception/sending direction indirectly, make main control chip (CPU) need not the control of individual processing data flow direction.
First voltage comparator U4A of plastic drive circuit 41 and the second voltage comparator U4B of data sending controling circuit 42 can be the same chips with two or more voltage comparators, as the LM293 chip of NS company.
Fig. 7 is the circuit theory diagrams of the bus interface circuit 44 of communication interface module 40, and this circuit suppresses diode TVS by the 6th pull-up resistor R51, pull down resistor R52, the 3rd current-limiting resistance R53, the 4th current-limiting resistance R54, transition and forms.Wherein pull-up resistor R51 is connected between the positive output end A pin of bus differential signal of power supply VCC2 and communication interface chip, plays the effect of drawing on the signal.Pull down resistor R52 is connected between the negative output terminal B pin of bus differential signal of ground GND2 and communication interface chip, plays the drop-down effect of signal.The 3rd current-limiting resistance R53 is connected between the positive output end A pin of bus differential signal of anodal RS+ of bus and communication interface chip, and the 4th current-limiting resistance R54 is connected between the negative output terminal B pin of bus differential signal of bus negative pole RS-and communication interface chip.The resistance of the 3rd current-limiting resistance R53 and the 4th current-limiting resistance R54 approximately is about 10 ohm, in order to the current-limiting protection effect.Transition suppresses diode TVS and is connected in parallel between anodal RS+ of bus and the bus negative pole RS-, is used to absorb hard pulse interference signal and surging signal between bus, thereby plays a protective role.Here, transition suppresses diode TVS and also can use device such as solid discharging tube to substitute.
Above-mentioned embodiment only is used to explain the present invention, rather than limitation of the present invention.
Claims (6)
1, a kind of RS485 communicating circuit, comprises main control chip (20), signal photoelectric isolation module (30) and communication interface module (40) at power isolation module (10); Wherein, described power isolation module (10) produces the 5V insulating power supply, is used for described communication interface module is powered, and makes described communication interface module (40) and described main control chip (10)) carry out isolated from power; Described signal photoelectric isolation module (30) comprises that data reception signal optically coupled isolation circuit (31) and data send flashlight buffer circuit (32), described data reception signal optically coupled isolation circuit (31) is connected with described communication interface module (40) with described main control chip (20) respectively, be used for the data that described communication interface module (40) is received from the RS485 bus interface are isolated, and be sent to the data-signal receiving terminal (RXD) of described main control chip (20); Described data send flashlight buffer circuit (32) and are connected with described communication interface module (40) with described main control chip (20) respectively, be used for the transmission signal of the data-signal transmitting terminal (TXD) of described main control chip (20) is isolated, and be transferred to described communication interface module (40);
It is characterized in that: described communication interface module (40) comprises received signal plastic drive circuit (41), data sending controling circuit (42), RS485 communication interface chip (43) and bus interface circuit (44); The input of described received signal plastic drive circuit (41) is connected with the data output end (R) of described RS485 communication interface chip (43), the output of described received signal plastic drive circuit (41) is connected with described data reception signal optically coupled isolation circuit (31), and the output signal of the data output end (R) of described RS485 communication interface chip (43) is carried out waveform shaping; The input of described data sending controling circuit (42) sends flashlight buffer circuit (32) with described data and is connected, the output of described data sending controling circuit (42) is connected with the Data Receiving/transmission Enable Pin (RE/DE) and the data input pin (D) of described RS485 communication interface chip respectively, finishes the transmission to bus interface circuit of the automatic control of described RS485 communication interface chip reception/sending direction and data; The input of described bus interface circuit (44) is connected with the bus difference output end of described RS485 communication interface chip (A, B), and the output of described bus interface circuit is connected with on-the-spot RS485 bus.
2, RS485 communicating circuit according to claim 1, it is characterized in that: described received signal optically coupled isolation circuit (31) comprises first pull-up resistor (R11), first current-limiting resistance (R12) and first optocoupler (U1), signal from described received signal plastic drive circuit (41) passes through the input that described first current-limiting resistance (R12) is connected to described first optocoupler (U1), and the output of described first optocoupler (U1) is connected to the data-signal receiving terminal (RXD) of described main control chip (20) through described first pull-up resistor (R11).
3, RS485 communicating circuit according to claim 1, it is characterized in that: described transmission flashlight buffer circuit (32) comprises second pull-up resistor (R21), second current-limiting resistance (R22) and second optocoupler (U2), be connected to the input of described second optocoupler (U2) from the signal of the data-signal transmitting terminal (TXD) of described main control chip (20) through described second current-limiting resistance (R22), the output of described second optocoupler (U2) is connected to the data sending controling circuit (42) of described communication interface module (40) through described second pull-up resistor (R21).
4, RS485 communicating circuit according to claim 1 is characterized in that: described received signal plastic drive circuit (41) comprises first divider resistance (R30), second divider resistance (R31), the 3rd pull-up resistor (R32), the 4th pull-up resistor (R33) and first voltage comparator (U4A);
The output signal of described communication interface chip (43) is through after drawing on described the 3rd pull-up resistor (R32), insert the positive input terminal of described first voltage comparator (U4A), described the 3rd pull-up resistor (R32) is connected between the data output end (R) of described 5V insulating power supply (VCC2) and described RS485 communication interface chip (43), described first divider resistance (R30) and described second divider resistance (R31) are series between described 5V insulating power supply (VCC2) and the ground (GND2), and the tie point between described first divider resistance (R30) and described second divider resistance (R31) is received the negative input end of described first voltage comparator (U4A); The output of described first voltage comparator (U4A) is through after drawing on described the 4th pull-up resistor (R33), be connected to described data reception signal optically coupled isolation circuit (31), described the 4th pull-up resistor (R33) is connected between the output of described 5V insulating power supply (VCC2) and described first voltage comparator (U4A).
5, RS485 communicating circuit according to claim 1 is characterized in that: described data sending controling circuit (42) comprises the 3rd divider resistance (R40), the 4th divider resistance (R41), the 5th pull-up resistor (R42) and second voltage comparator (U4B);
Described the 3rd divider resistance (R40) and described the 4th divider resistance (R41) are connected between described 5V insulating power supply (VCC2) and the ground (GND2), and described the 5th pull-up resistor (R42) is connected between the output of described 5V insulating power supply (VCC2) and described second voltage comparator (U4B); Import the negative input end of described second voltage comparator (U4B) from the signal of described data transmission flashlight buffer circuits (32), be input to the data input pin (D) of described RS485 communication interface chip (43) simultaneously, the level that described the 3rd divider resistance (R40) and described the 4th divider resistance (R41) dividing potential drop form is input to the positive input terminal of described second voltage comparator (U4B), and the output of described second voltage comparator (U4B) is connected to the Data Receiving/transmission Enable Pin (RE/DE) of described RS485 communication interface chip (43).
6, RS485 communicating circuit according to claim 1 is characterized in that: described bus interface circuit (44) suppresses diode (TVS) by the 6th pull-up resistor (R51), pull down resistor (R52), the 3rd current-limiting resistance (R53), the 4th current-limiting resistance (R54), transition and forms;
Wherein said the 6th pull-up resistor (R51) is connected between the positive output end (A) of bus differential signal of described 5V insulating power supply (VCC2) and described RS485 communication interface chip, plays the effect of drawing on the signal; Described pull down resistor (R52) is connected between the negative output terminal (B) of bus differential signal of ground (GND2) and described RS485 communication interface chip (43), plays the drop-down effect of signal; Described the 3rd current-limiting resistance (R53) is connected between the positive output end (A) of bus differential signal of the positive pole (RS+) of described on-the-spot RS485 bus and described RS485 communication interface chip (43), and described the 4th current-limiting resistance (R54) is connected between the negative output terminal (B) of bus differential signal of the negative pole (RS-) of described on-the-spot RS485 bus and described RS485 communication interface chip (43); Described transition suppresses diode (TVS) and is connected in parallel between the positive pole (RS+) and negative pole (RS-) of described on-the-spot RS485 bus, is used to absorb hard pulse interference signal and surging signal between bus.
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