CN110943900B - Carrier monitoring multi-access RS485 bus circuit with collision detection and method - Google Patents
Carrier monitoring multi-access RS485 bus circuit with collision detection and method Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
- H04L12/407—Bus networks with decentralised control
- H04L12/413—Bus networks with decentralised control with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
- G06F13/14—Handling requests for interconnection or transfer
- G06F13/16—Handling requests for interconnection or transfer for access to memory bus
- G06F13/1605—Handling requests for interconnection or transfer for access to memory bus based on arbitration
- G06F13/161—Handling requests for interconnection or transfer for access to memory bus based on arbitration with latency improvement
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
- G06F13/38—Information transfer, e.g. on bus
- G06F13/40—Bus structure
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Abstract
The invention relates to a carrier monitoring multi-access RS485 bus circuit with collision detection and a method thereof, wherein the carrier monitoring multi-access RS485 bus circuit comprises a first RS485 chip and a second RS485 chip; the first RS485 chip is used for receiving and transmitting data, and the second RS485 chip is used for carrier monitoring and collision detection of the bus. The invention adds the functions of carrier monitoring and conflict detection on the basis of the traditional RS485 bus, and directly controls the RS485 receiving and transmitting pin to stop transmitting by a hardware circuit after detecting the bus conflict without software intervention, thereby having high response speed.
Description
Technical Field
The invention relates to the field of RS485 buses, in particular to a carrier monitoring multi-access RS485 bus circuit with collision detection and a method thereof.
Background
The RS485 bus is widely applied to the field bus by the advantages of simple structure, low manufacturing cost, long transmission distance, convenience in maintenance and the like. The RS485 bus uses a twisted pair as a physical medium and works in a half-duplex communication mode, namely, only one node on the bus is in a transmitting state at the same time, and other nodes are in a receiving state. The RS485 works in a master-slave mode generally, and comprises a master node and a plurality of slave nodes, wherein the master node polls and inquires data of the slave nodes continuously. Due to the adoption of a polling mode, the real-time performance of data is poor, and the requirement of real-time uploading of alarm data cannot be met. If the polling interval is reduced, although the data real-time performance is improved to a certain extent, for a system with a high requirement on low power consumption, the nodes in the dormant state are frequently awakened, and the power consumption of the system is increased. Therefore, for a system with low power consumption and high real-time requirement, the RS485 bus cannot meet the application requirement.
Disclosure of Invention
In view of the above, the present invention aims to provide a carrier sense multiple access RS485 bus circuit with collision detection and a method thereof, which add carrier sense and collision detection functions on the basis of the conventional RS485 bus, and directly control an RS485 receive-transmit pin to stop transmitting by a hardware circuit after detecting bus collision, without software intervention, and with high response speed.
In order to achieve the purpose, the invention adopts the following technical scheme:
a carrier monitoring multi-access RS485 bus circuit with collision detection comprises a first RS485 chip and a second RS485 chip; the first RS485 chip is used for receiving and transmitting data, and the second RS485 chip is used for carrier monitoring and collision detection of the bus.
Furthermore, the circuit also comprises an exclusive-or gate, a trigger, a first and gate, a second and gate and an inverter; a fourth pin DI of the first RS485 chip is connected with a second pin B of the exclusive-OR gate through a second resistor; a first pin RO of the second RS485 chip is connected with a first pin A of the exclusive-OR gate through a thirteenth resistor; a fourth pin Y of the exclusive-or gate is respectively connected with a first pin CLK of the trigger and the input end of the inverter after passing through a fourteenth resistor; a fourth pin Q and a sixth pin OE of the trigger are respectively connected with two input ends of the first AND gate; the output end of the first AND gate is connected with a third pin DE of the first RS485 chip through a fourth resistor; two input ends of the second AND gate are respectively connected with one end of an eighteenth resistor and the output end of the phase inverter; and the other end of the eighteenth resistor is connected with a fifth pin VCC of the trigger.
Furthermore, the circuit is connected with the MCU through 4 lines of MCU _ TX, MCU _ RX, MCU _ DR and MCU _ INT; the MCU _ TX is connected with a No. 4 pin DI of the first RS485 chip through a second resistor; the MCU _ TX is also connected to a second pin B of the exclusive-OR gate; the MCU _ RX is connected with a first pin RO of the first RS485 through an eighth resistor; the MCU _ DR is respectively connected with a sixth pin OE of the trigger and the input end of the first AND gate through R17; and the MCU _ INT is connected with the output end of the second AND gate.
A method for monitoring a multi-access RS485 bus circuit by carrier waves with collision detection comprises the following steps:
step S1: detecting the state of the bus through an MCU _ INT signal before data transmission, and if the bus is idle in continuous minimum time slots, judging that the bus is idle and entering data transmission;
step S2, monitoring the state of MCU _ INT signal at all times during data transmission, stopping transmitting data if detecting bus collision, switching MCU _ DR to receiving state, and recovering the MCU _ INT signal to idle state; and after the retransmission delay time is up, the data transmission is carried out again.
Further, the step S1 is specifically: before receiving data, carrying out carrier detection, if a bus is idle, Q is high, a first pin input CS1 of a trigger is low, a U inverter outputs CS2 to be high, and MCU _ INT is high; if data is transmitted and received on the bus, the CS2 will be low, the MCU _ INT will output low, which indicates that the bus is occupied and needs to delay the random time slot, and then data transmission is carried out; if the MCU continuously detects that the interval of 1 byte is kept at high level, the bus is considered to be idle, and data transmission is immediately carried out.
Further, the step S2 is specifically: during data transmission, the MCU _ DR inputs a high level. When a 0 is transmitted, the MCU _ TX is low, if the bus signal is 1, the MONITOR _ RX signal is high, the MCU _ TX and the MONITOR _ RX are respectively input into A, B of the exclusive-OR gate, the Y output of the exclusive-OR gate is changed from low to high, the CS1 rising edge signal is input into CLK of the trigger, the rising edge of the trigger is triggered, and the Q output of the pin is changed from high to low; the MCU _ DR of a pin 1 of the first AND gate is high, the Q of a pin 2 of the first AND gate is low, the UART _ DR output of the AND gate is low, the first RS485 chip is switched to a receiving state, and the transmission is stopped; pin Q of the second AND gate 1 is low, the output MCU _ INT of the second AND gate is kept low all the time, and the bus stops transmitting due to collision.
Further, the retransmission delay time is calculated by using a back-off algorithm, specifically:
retransmission delay = R minimum slot
Wherein, the minimum time slot is 1 byte of sending time; a random number R is generated based on the ID of the node device.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention has the functions of carrier monitoring and conflict detection, and after bus conflict is detected, the RS485 receiving and transmitting pin is directly controlled by a hardware circuit to stop transmitting without software intervention, so that the response speed is high.
2. The invention relates to a method for preparing a high-temperature-resistant ceramic material. Under the condition of ensuring the performance of the RS485 bus, the function of multiple hosts of the RS485 bus is realized.
Drawings
FIG. 1 is a circuit schematic of the present invention;
FIG. 2 is a flow chart of a control method according to an embodiment of the invention.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
Referring to fig. 1, the present invention provides a carrier sensing multiple access RS485 bus circuit with collision detection, including a first RS485 chip and a second RS485 chip; the first RS485 chip is used for receiving and transmitting data, and the second RS485 chip is used for carrier monitoring and collision detection of the bus.
In this embodiment, the circuit further includes an exclusive or gate, a flip-flop, a first and gate, a second and gate, and an inverter; a fourth pin DI of the first RS485 chip is connected with a second pin B of the exclusive-OR gate through a second resistor; a first pin RO of the second RS485 chip is connected with a first pin A of the exclusive-OR gate through a thirteenth resistor; a fourth pin Y of the exclusive-or gate is respectively connected with a first pin CLK of the trigger and the input end of the inverter after passing through a fourteenth resistor; a fourth pin Q and a sixth pin OE of the trigger are respectively connected with two input ends of the first AND gate; the output end of the first AND gate is connected with a third pin DE of the first RS485 chip through a fourth resistor; two input ends of the second AND gate are respectively connected with one end of an eighteenth resistor and the output end of the phase inverter; and the other end of the eighteenth resistor is connected with a fifth pin VCC of the trigger.
In the embodiment, the circuit is connected with the MCU through 4 lines of MCU _ TX, MCU _ RX, MCU _ DR and MCU _ INT; the MCU _ TX is connected with a No. 4 pin DI of the first RS485 chip through a second resistor; the MCU _ TX is also connected to a second pin B of the exclusive-OR gate; the MCU _ RX is connected with a first pin RO of the first RS485 through an eighth resistor; the MCU _ DR is respectively connected with a sixth pin OE of the trigger and the input end of the first AND gate through R17; and the MCU _ INT is connected with the output end of the second AND gate. The MCU _ TX is used for RS485 data transmission. MCU _ RX is used for RS485 data reception. The MCU _ DR is used for receiving and transmitting control of the RS485 chip, and high level is used for sending data and low level is used for receiving data. And the MCU _ INT reflects the state of the RS485 bus, and outputs a low level if the bus is busy or conflicts, and outputs a high level if the bus is idle.
In this embodiment, a method for monitoring a multiple-access RS485 bus circuit with collision detection by a carrier includes the following steps:
step S1: firstly, carrying out carrier detection; if the bus is idle, Q is high, CS1 is low, CS2 is high through U7 inverter, MCU _ INT is high; if data is transmitted and received on the bus, the CS2 will be low, the MCU _ INT will output low, which indicates that the bus is occupied and the random time slot needs to be delayed, and then data transmission is carried out. If the MCU continuously detects that the interval of 1 byte is kept at high level, the bus is considered to be idle, and data transmission is immediately carried out.
In step S2, the MCU _ DR inputs a high level during data transmission. When transmitting '0', the MCU _ TX is low, if the bus signal is '1', the MONITOR _ RX signal is high, the MCU _ TX and the MONITOR _ RX are respectively input to a A, B pin of an exclusive-OR gate (U3), the Y output of the exclusive-OR gate (U3) is changed from low to high, a CS1 rising edge signal is input to CLK of a D flip-flop (U4), a D flip-flop (U4) rises to trigger, and the Q pin output is changed from high to low. And gate (U5A) 1 pin MCU _ DR is high, 2 pin Q is low, and AND gate (U5A) output UART _ DR is low, switches RS485 chip (U1) to receiving state, stops transmitting. Pin Q of and gate (U5B) 1 is low, and MCU _ INT output by and gate (U5B) remains low all the time, and bus transmission is stopped due to bus collision.
When the MCU detects that the MCU _ INT is low level in the transmitting process, the RS485 interface circuit stops transmitting because of bus collision. MCU stops transmitting, and output MCU _ DR is low, D flip-flop (U4)/OE input is low, Q output of D flip-flop (U4) is high, Q signal is high. The circuit re-enters the carrier sense state. The MCU delays the random time slot to detect the bus state again according to a simplified back-off algorithm, and data retransmission is carried out.
The bus state is detected by the MCU _ INT signal before data transmission. And if the continuous minimum time slots are idle, judging that the bus is idle. And entering data transmission, monitoring the state of the MCU _ INT signal at all times in the data transmission process, stopping transmitting data if bus collision is detected, switching the MCU _ DR to a receiving state, and recovering the MCU _ INT signal to an idle state. And after the retransmission time is up, the data transmission is carried out again.
In this embodiment, the retransmission delay time is calculated by using a back-off algorithm, specifically:
retransmission delay = R minimum slot
Wherein, the minimum time slot is 1 byte of sending time; and generating a random number R according to the ID of the node equipment, wherein the value range of R is (0-255).
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (6)
1. A carrier monitoring multi-access RS485 bus circuit with collision detection is characterized by comprising a first RS485 chip and a second RS485 chip; the first RS485 chip is used for receiving and transmitting data, and the second RS485 chip is used for carrier monitoring and collision detection of a bus; the circuit also comprises an exclusive-OR gate, a trigger, a first AND gate, a second AND gate and a phase inverter; a fourth pin DI of the first RS485 chip is connected with a second pin B of the exclusive-OR gate through a second resistor; a first pin RO of the second RS485 chip is connected with a first pin A of the exclusive-OR gate through a thirteenth resistor; a fourth pin Y of the exclusive-or gate is respectively connected with a first pin CLK of the trigger and the input end of the inverter after passing through a fourteenth resistor; a fourth pin Q and a sixth pin OE of the trigger are respectively connected with two input ends of the first AND gate; the output end of the first AND gate is connected with a third pin DE of the first RS485 chip through a fourth resistor; two input ends of the second AND gate are respectively connected with one end of an eighteenth resistor and the output end of the phase inverter; and the other end of the eighteenth resistor is connected with a fifth pin VCC of the trigger.
2. The RS485 bus circuit with carrier sensing multiple access for collision detection according to claim 1, wherein the circuit is connected to MCU via MCU _ TX, MCU _ RX, MCU _ DR and MCU _ INT 4 lines; the MCU _ TX is connected with a No. 4 pin DI of the first RS485 chip through a second resistor; the MCU _ TX is also connected to a second pin B of the exclusive-OR gate; the MCU _ RX is connected with a first pin RO of the first RS485 through an eighth resistor; the MCU _ DR is respectively connected with a sixth pin OE of the trigger and the input end of the first AND gate through R17; and the MCU _ INT is connected with the output end of the second AND gate.
3. The method for controlling the RS485 bus circuit with collision detection and carrier sensing multiple access according to claim 2, comprising the following steps:
step S1: detecting the state of the bus through an MCU _ INT signal before data transmission, and if the bus is idle in continuous minimum time slots, judging that the bus is idle and entering data transmission;
step S2, monitoring the state of the MCU _ INT signal every minimum time slot or by interruption in the data transmitting process, stopping transmitting data if detecting bus collision, switching the MCU _ DR to a receiving state, and recovering the MCU _ INT signal to an idle state; and after the retransmission delay time is up, the data transmission is carried out again.
4. The method for controlling the RS485 bus circuit with collision detection and carrier sensing multiple access according to claim 3, wherein the step S1 specifically includes: before receiving data, carrying out carrier detection, if the bus is idle, Q is high, a first pin input CS1 of the trigger is low, a U inverter outputs CS2 to be high, and MCU _ INT is high; if data is transmitted and received on the bus, the CS2 will be low, the MCU _ INT will output low, which indicates that the bus is occupied and needs to delay the random time slot, and then data transmission is carried out; if the MCU continuously detects that the interval of 1 byte is kept at high level, the bus is considered to be idle, and data transmission is immediately carried out.
5. The method for controlling the RS485 bus circuit with collision detection and carrier sensing multiple access according to claim 3, wherein the step S2 specifically includes: in the process of sending data, the MCU _ DR inputs a high level;
when a 0 is transmitted, the MCU _ TX is low, if the bus signal is 1, the MONITOR _ RX signal is high, the MCU _ TX and the MONITOR _ RX are respectively input into A, B of the exclusive-OR gate, the Y output of the exclusive-OR gate is changed from low to high, the CS1 rising edge signal is input into CLK of the trigger, the rising edge of the trigger is triggered, and the Q output of the pin is changed from high to low; the MCU _ DR of a pin 1 of the first AND gate is high, the Q of a pin 2 of the first AND gate is low, the UART _ DR output of the AND gate is low, the first RS485 chip is switched to a receiving state, and the transmission is stopped; pin Q of the second AND gate 1 is low, the output MCU _ INT of the second AND gate is kept low all the time, and the bus stops transmitting due to collision.
6. The method for controlling the RS485 bus circuit with collision detection and carrier sensing multiple access according to claim 3, wherein the retransmission delay time is calculated by a back-off algorithm, specifically:
retransmission delay = R minimum slot
Wherein, the minimum time slot is 1 byte of sending time; a random number R is generated based on the ID of the node device.
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| CN111314190A (en) * | 2020-04-15 | 2020-06-19 | 联合华芯电子有限公司 | Data transmission system and method with arbitration interface having reset function |
| CN112597084B (en) * | 2020-12-31 | 2022-06-24 | 杭州拓深科技有限公司 | System for two-wire system solves many main arbitration of RS485 and collides |
| CN114374579B (en) * | 2022-01-14 | 2023-04-28 | 宁波迦南智能电气股份有限公司 | RS485 bus competition type communication method |
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