CN111385178A

CN111385178A - RS422 bus link monitoring and network failure protection system

Info

Publication number: CN111385178A
Application number: CN201911348287.6A
Authority: CN
Inventors: 凌永锋
Original assignee: Chengdu Guoyi Electronic Technology Co ltd
Current assignee: Chengdu Guoyi Electronic Technology Co ltd
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2020-07-07

Abstract

The invention discloses a RS422 bus link monitoring and network failure protection system, which comprises; the switch control unit is used for switching the working state of the circuit; the network failure protection unit avoids the bus network from being in a paralyzed state, and solves the failure protection problem under the condition of bus short circuit; the bypass direct connection unit is used for realizing hardware bypass direct connection between the devices; the level conversion circuit is used for realizing level conversion; and the CPU control unit monitors link data, transmits backup data and controls the transmission of the multi-main bus. The invention realizes RS422 bus link monitoring and data recording between point-to-point devices. Meanwhile, the hardware communication circuit realizes real-time data transmission, and the network failure protection unit avoids the bus network from being in a paralysis state, ensures the communication between important equipment and ensures the real-time performance and the reliability of the system.

Description

RS422 bus link monitoring and network failure protection system

Technical Field

The invention relates to the field of RS422 bus communication, in particular to an RS422 bus monitoring and network failure protection system.

Background

The RS422 standard is collectively referred to as "balanced voltage digital interface circuit electrical characteristics" which define the characteristics of the interface circuit. RS422 is full duplex communication, both parties of which contain one transmit driver and one receive driver. Where the two balanced line connection terminals of the receive driver are defined as a and B and the two balanced line connection terminals of the transmit driver are defined as Y and Z, Y and A, Z and B at one end are typically connected using balanced twisted pair wires. Normally, the positive level between the transmit driver terminals Y, Z is between +2 and +6V, representing positive logic, and the negative level is between-6 and-2V, representing negative logic. At the receiving end, when the A, B has a level larger than +200mV, a positive logic level is output, and when the level is smaller than-200 mV, a negative logic level is output. The maximum transmission distance of the RS422 is 4000 feet (about 1219 m) and the maximum transmission rate is 10 Mb/s. The length of the balanced twisted pair is inversely proportional to the transmission rate, and the maximum transmission distance can be reached at the rate of 100 Kb/s. The highest rate of transmission is only obtained at short distances. A typical maximum transmission rate of 1Mb/s can be achieved with 100 meters long twisted pair.

According to the related standard of RS-422, the RS-422 bus is a point-to-multipoint communication mode, namely only one sending end is provided at the same time, and a plurality of receiving ends are provided at the same time. If the first master device and the second master device complete point-to-point communication, the receiving end of the bypass device performs link monitoring on the bus. The operation flow of the prior art is that an important first main road device sends a command to a second main road device, and the second main road device responds to the command of the first main road device; and the second main road device sends a command to the first main road device, and the first main road device responds to the command of the second main road device. The bypass device can only receive data as a slave device. The defects of the prior art are as follows:

1. monitoring a bypass device parallel bus to reduce the logic level of the bus, and simultaneously, the abnormal working state may cause the bus paralysis to influence the data communication between the important first main device and the second main device;

2. switching data forwarding by a signal relay or an analog switch cannot realize real-time data forwarding, so that communication delay is caused;

3. the RS-422 standard specifies a receiver threshold of 200 mV. This provides for a relatively high noise suppression capability, as previously described, when the receiver a level is +200mV or more higher than the B level, the output is positive logic, and vice versa. However, due to the existence of the third state, that is, after the host sends an information data at the transmitting end, the bus is put into the third state, that is, no signal drives the bus when the bus is idle, so that the voltage between the AB is between-200 mV and +200mV and tends to 0V, which brings a problem: the receiver output state is uncertain. If the output of the receiver is 0V, the slave in the network will interpret it as a new start bit and try to read the following byte, since there is never a stop bit, resulting in a frame error result, no more devices requesting the bus, and the network is in a state of paralysis. In addition to the above-described situation where bus idleness causes the two wires to be less than 200mV, this can also occur in open or short circuits.

Disclosure of Invention

The invention aims to provide a system for monitoring RS422 bus link and protecting network failure in order to solve the problems.

The invention aims to be realized by the following technical scheme: an RS422 bus link snooping and network failure protection system, comprising:

the switch control unit is used for realizing data transmission between main road equipment on a through link, realizing the link through in a default state through the switch closing characteristic, and enabling the first main road equipment and the second main road equipment to be in bidirectional through connection through the through link when the bypass equipment does not work; the snooping devices are not directly connected in parallel to the bus, and the working state of the snooping devices does not influence the logic level of the bus.

The level shifter circuit implements TX and RX that level-shift RS422 to TTL levels.

The network failure protection unit fixes the logic level, determines the bus state, avoids the bus network from being in a paralyzed state, ensures the communication between important equipment and ensures the real-time performance and the reliability of the system.

The bypass direct-connection unit realizes the direct connection of the hardware links of the first main road device and the second main road device, data can reach the devices of both communication sides in a bypass direct-connection mode, time delay of software data forwarding is avoided, and data real-time performance is guaranteed.

The CPU control unit receives and monitors data transmission of the first main road device and the second main road device.

The two-way receiving Buffer chip adopts a parallel circuit, and one way of the chip is connected to the bypass backup unit and is used for sending data between the first main path equipment and the second main path equipment; and the other path is connected to the CPU control unit and is used for realizing the monitoring of the link data.

The invention has the beneficial effects that:

1. the default through switch control circuit ensures the data link of the important first main road device and the important second main road device, and the working state of the bypass device does not influence the bus;

2. the bypass backup unit realizes pure hardware direct connection, data can reach devices of both communication sides in a bypass direct connection mode, the time delay level is nS level, time delay of software data forwarding is avoided, and data real-time performance is guaranteed;

3. the network failure protection unit is adopted to bias the bus in a determined state by using a fixed logic level when the bus is idle or open-circuit, so as to avoid the bus network from being in a paralysis state. And the receiving threshold is shifted to-200 mV/-50mV, thus solving the problem of failure protection under the condition of bus short circuit.

Drawings

FIG. 1 is a schematic block diagram of the architecture of the present invention;

fig. 2 is a data flow diagram of a main device and a bypass device in the present invention.

Detailed Description

In order to more clearly understand the technical features, objects and effects of the present invention, embodiments of the present invention will be described with reference to the accompanying drawings.

In this embodiment, as shown in fig. 2, an RS422 bus link monitoring and network failure protection system includes a switch control unit, a network failure protection unit, an asynchronous RS422 conversion TX unit, an asynchronous RS422 conversion RX unit, a bypass direct connection unit, and a CPU control unit.

The switch control unit ensures that the default link is in direct connection through the closed characteristic of the switch, and when the bypass equipment does not work, the direct connection path enables the first main road equipment and the second main road equipment to be in direct connection in a data bidirectional mode. The snooping devices are not directly connected in parallel to the bus, and the working state of the snooping devices does not influence the logic level of the bus.

The network failure protection unit is used for biasing the bus in a determined state by using a fixed logic level when the bus is idle or open-circuit, so that the bus network is prevented from being in a paralysis state. And the receiving threshold is shifted to-200 mV/-50mV, thus solving the problem of failure protection under the condition of bus short circuit.

The asynchronous RS422 converts the TX unit and the RS422 converts the RX unit, receives the level sent out on the through link or the CPU control unit, and converts it into TX and RX of the TLL level.

The bypass direct connection ensures that the hardware link direct connection of the first main road device and the second main road device is realized, data can reach the devices of both communication sides in a bypass direct connection mode, the time delay of software data forwarding is avoided, and the real-time performance of the data is ensured.

The CPU control unit receives the level converted by the asynchronous RS422 conversion unit through a CPU receiving end of the bypass device, controls the bypass device to monitor and back up the bus link, and sends the backed-up monitoring data to the first main road device and the second main road device which receive the data when the bus link data is completely sent and the bus is released, so that the integrity of the data is ensured.

In the embodiment, the RS422 bus link monitoring and network failure protection unit is realized, the bypass backup unit is purely in hardware direct connection, data is sent to communication equipment without delay, and the real-time performance of the data is ensured; meanwhile, a network failure protection unit is adopted, the bus is kept in a determined state by using a fixed logic level, the network breakdown of the bus is avoided, and the failure protection problem caused by the short circuit of the bus is solved.

In this embodiment, the specific system principle analysis is as follows:

1. and through the switch closing characteristic, the default through path is ensured to be straight through. That is, when the bypass device is not operating, the pass-through path enables the first master device to pass through the second master device data in a bi-directional manner. The snooping devices are not directly connected in parallel to the bus, and the working state of the snooping devices does not influence the logic level of the bus.

2. When the bypass equipment works, the switch switching circuit works, and the bus through link is disconnected. The first main road device and the second main road device respectively send data through the two-way receiving Buffer chip, one way of data is directly sent to the other side through the hardware bypass, real-time data forwarding is achieved, and the other way of data is sent to the receiving end of the CPU of the bypass device, and link data monitoring is achieved.

3. The network failure protection unit fixes the logic level, biases the bus in a determined state, and avoids the bus network from being in a paralysis state. And the receiving threshold is shifted to-200 mV/-50mV, thus solving the problem of failure protection under the condition of bus short circuit.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. An RS422 bus link monitoring and network failure protection system, which comprises a first main road device and a second main road device connected by a direct link, and is characterized by comprising:

the switch control unit is arranged on the direct connection link, controls link transmission between the first main road device and the second main road device, and realizes link direct connection in a default state and mutual communication between the devices through the switch closing characteristic;

the bypass equipment is in communication connection with the straight-through link through the level conversion circuit, so that data receiving and data monitoring of the main equipment are realized;

the level conversion circuit is connected with the through link and the bypass equipment to realize level signal conversion and transmission between the through link and the bypass equipment;

and the network failure protection unit is arranged between the direct link and the level conversion circuit, realizes data transmission between the devices, avoids network breakdown from passing through a fixed logic level, determines a bus bias state, avoids the bus network from falling into the breakdown state, ensures communication between important devices, and ensures the real-time performance and the reliability of the system.

2. The RS422 bus link monitoring and network failure protection system of claim 1, wherein the bypass device includes a bypass pass-through unit, the bypass pass-through unit implements hardware link pass-through of the first master device and the second master device, data can reach devices of both communication parties by bypass pass-through, there is no time delay of software data forwarding, and data real-time is guaranteed.

3. The RS422 bus link snooping and network failure protection system of claim 1, wherein the bypass device includes a CPU control unit, the CPU control unit receives and snoops data transmission of the first master device and the second master device.

4. The RS422 bus multi-master device link control system of claim 1, further comprising a two-way receiving Buffer chip, the chip employs a parallel circuit, one way is connected to the bypass backup unit, for data transmission between the first master device and the second master device; and the other path is connected to the CPU control unit and is used for realizing the monitoring of the link data.