What Is Digital Signage?

Wikipedia gives its definition as below: Digital signage is a sub-segment of electronic signage. Digital displays use technologies such as LCD, LED, projection and e-paper to display digital images, video, web pages, weather data, restaurant menus, or text.

5G/4G LTE Wireless Digital Signage Solution

The traditional way of providing internet access for updating content for digital signage solution is to use landline, while this makes challenges for media operators and advertiser to quickly expand their deployment, because it costs them money and time to get landline cable, and not easy and convenient to manage and monitor the status of massive digital signage deployed national wide or globally. Thanks to the fast development of 4G LTE technology, things have been changed, using the 5G/4G wireless network to transfer the content remotely has become the mainstream technology of connectivity.

Although USB modems and home use routers are still used as a wireless internet access, however, Bivocom industrial cellular router have more advantages as below.

1. Reliable and robust connectivity
2. Openwrt based Linux OS allows for secondary development
3. With industrial IO like relay output to hard restart the front digital signage system remotely
4. Device management platform for monitoring the status of routers
5. VPN and Radius WIFI provides secure and private tunnel and maintenance

From below diagram, you’ll learn why using industrial cellular router over USB modems or consumer routers are important, as without a reliable and stable connectivity between your digital display and remote content platform, you couldn’t update and contents timely, which will deliver poor service to companies who pay for the advertisement.

Today, we’re going to share with you 4 typical applications of digital signage that using Bivocom 4G LTE IoT routers as a main connectivity between remote site and server for content update.

1. Outdoor LED Display Advertisement Roadside

A UK solution provider of digital signage is looking for embedded industrial 4G cellular router to build the PCB board of router to their control box, and Thanks to Bivocom fast and flexible customized R&D service, we quickly design a customized embedded 4G LTE IoT router board which is a great fit to customer’s control box.

2. LED Digital Road Sign

A system integrator of digital road sign is looking for an industrial cellular router that comes with

1. Dual SIM for failover with different operators
2. GPS for location positioning
3. Radius WIFI for secure maintenance

Bivocom industrial 4G cellular router TR341 is a great fit for customer, which also comes with RS485, RS232 for weather status sensor to display the weather condition.

3. LCD Advertisement Display for Toilet of hotel

A system integrator in Asia is specializing on providing LCD display advertisement solution for toilet for hotel, shopping center, and they have headache of using home use router, because it couldn’t provide reliable and robust connectivity, and they couldn’t do remote monitor and manage of their routers, so Bivocom recommends TR341 that comes with dual sim and WIFI.

     4. Outdoor LED Display for Smart Pole

A solution provider of smart pole in China is looking for industrial grade IoT gateway that comes with digital input, analog input, RS232, RS485, Ethernet ports, relay output for their smart pole project for a park. Bivocom recommends the industrial edge gateway TG452, which has the interfaces customer requires, besides, its 1GB flash and ARM based CPU, with protocols like Modbus RTU/TCP, MQTT, JSON, allows customer to collect, process, analysis at the edge and store the data too, which save bandwidth for remote server.

If you haven’t found the right 5G/4G wireless routers for your application, please contact Bivocom experts.

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Wikipedia gives air compressor definition as below.

An air compressor is a pneumatic device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When the tank’s pressure reaches its engineered upper limit, the air compressor shuts off. The compressed air, then, is held in the tank until called into use. The energy contained in the compressed air can be used for a variety of applications, utilizing the kinetic energy of the air as it is released and the tank depressurizes. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank. An air Compressor must be differentiated from a pump because it works for any gas/air, while pumps work on a liquid.

There are two main designs for the majority of air compressors: reciprocating piston air compressors and rotary screw air compressors.

Who Uses Air Compressors?

Air compressors have been widely used in many industries and applications, and different application calls for different type of air compressors. Air compressors can be grouped into three classifications: consumer grade, professional grade and industrial grade

1. Consumer Grade

Small and portable air compressors that we’re using in our daily life, such as, air compressor pumps to inflate vehicle and bicycle tyres, or pressure washing, spray painting, etc.

Inflating and Spray Painting

2. Professional Grade

Construction may use the air compressor to power the drills, hammers and compactors, while for agriculture or farming, the air compressors have been used to power tractors, sprayers, pumps, and crop conveyors.

Construction and Farming

3. Industrial grade

For manufacturing, air compressors are used to power the conveyor belts, sprayers, presses, and packaging. Besides, application like Heating, Ventilation and Air Conditioning (HVAC), Rotary screw air compressors conduct vapour compression refrigeration that entails compressing air vapours, raising the temperature, and modulating the all-important refrigerant cycles. Oil drilling relies on air compressors for functionality in the energy sector.

Manufacturing and HVAC

Air Compressor Remote Monitor System In Crude Oil Production

Today, we’re going to share with you a case study using Bivocom industrial 4g cellular IoT router TR321 for remote monitoring and managing air compressors that are used in crude oil production in USA. The air compressor is used to pull the natural gas from oil storage tank and put it in gas pipeline, so instead of burning it all, the oil company can compress and put it in the natural gas pipeline, and together with a VRU(Vapor Recovery Unit) system, it helps to prevent emissions vented to the atmosphere, and save money for oil companies.

TR321/Air Compressor

Bivocom TR321 is a compact designed industrial grade 4g cellular IoT router, with interfaces of RS232, RS485 and RJ45 for diverse type of controllers, sensors, and it supports industrial protocols, like Modbus RTU/TCP, and able to convert Modbus data to JSON and transfer it over MQTT via 4G/3G/2G. It has been widely used in industry 4.0, digital signage, IP camera, vending machines, ATM, EV charging points, solar power, etc.

The post How 4G&IoT Helps to Remote Monitor Air Compressor in Oil Production appeared first on Bivocom.

1. What is JSON

JSON (JavaScript Object Notation) is a lightweight data exchange format. Easy to read and write. At the same time, it is easy to parse and generate by machine.

2. Why choose JSON

When we want to transmit multiple sets of IoT node attribute information, we can package and republish the data, and unpackage the data on the subscription side. The advantage of this is: determine which attribute the information we subscribe to belongs to, and prevent the information from being Wrongly attributed to other attributes to ensure the accuracy of the information. JSON provides us with a good data encoding format. The use of MQTT + JSON for IoT communication has become the main method for major IoT platforms.

3.  Setting up JSON protocol of PCCom Industrial Gateway

1.  Connect the edge computing gateway of CTC through a network cable, enter the gateway management system (192.168.1.1), select the data collection setting column in the gateway management system, and enter the server configuration interface.

1. In the server configuration interface, select the JSON configuration parameters, as shown in the red box in the following figure:
2.  Set parameters such as custom variable name, custom variable value, time stamp, equipment number, factor and factor data, equipment number, etc. in the management system.

The reporting format is as follows:

JSON data format

Custom variable name: publish id, as shown above

Top definition variable value: terminal serial ID, as shown above

Ts: Timestamp

Params: parameters, use curly brackets to include device number, factor and factor data

DeviceNum: device number

The format of the JSON body reported by the TG462 Industrial Gateway TG462 can be flexibly adjusted according to actual needs. The collection process can also support various methods such as reporting from time to time, reporting periodically, reporting changes, and reporting alarms. At the same time, it supports powerful edge computing, which can process data at the edge to ensure data security.

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Today, people use smart phone to make voice and video call, send email to communicate with their family, colleagues, friends and customers, as well as read daily news, edit documents, etc.

Just like human beings, in IoT(Internet of Things) world, machines also need their own “smart phone” to transfer and exchange the data. And the “smart phone” that used in IoT world includes, industrial cellular modems, routers, gateways.

1. Where are industrial cellular modems and gateways used?

Industrial modems and gateways are mainly used in industrial automation, energy and utilities (gas, oil, water, power), smart city (smart EV charging stations, smart pole), agriculture, environment, transportation, retail (digital signage, POS) , etc.

2. Why do you need an industrial cellular modem or gateway for your IoT project?

• Provide robust and reliable IoT connectivity
• Make your IoT project easy and flexible to install and manage
• Save cost on your infrastructure building

3. How to choose the right industrial cellular modems and gateways for your IoT project?

• Verify the interfaces of your field sensors, controllers

There are diverse of interfaces in sensors and controllers, such as, RS232, RS485, ethernet port (RJ45), digital input, digital output, relay, pulse input, I2C, etc.

• What cellular network to use?

The cellular network deployed by global telcos includes, 5G, 4G, 3G, 2G, LTE CAT M1, NB-IoT. To choose the right cellular technology for your IoT project will be related to below factors

1. How big of the data you want to transfer.

If you want to transfer the video stream, you may need 5G and 3G, while if your application is just for power meter reading, then 2G or LTE CAT M1, NB-IoT are good enough.

1. What cellular network and frequency your local Telcos provides

Different country and telco have their own frequency and coverage of cellular network, you’ll need to figure out where your IoT sensors, controllers are installed.

1. Your budget of data plan for SIM card

If your IoT project requires small data transmission, and your country has LTE CAT M1, or NB-IoT, and you don’t have to use 4G LTE, or 3G.

• What protocols and features your IoT project requires

Protocols like Modbus RTU/TCP, MQTT, VPN(PPTP, L2TP, IPsec, and GRE) are very common is today’s industrial cellular routers and gateways.

• Can the routers or gateways provide you a reliable, robust and secure connectivity?  

Does the router or gateway support dual sim for failover, or failover between wired and wireless? And does it support VPN security? Is the router industrial grade, or it’s just for consumer clients?

• What R&D and technical support you can get from the manufacturer?

IoT world’s needs are changing so fast that there is not a standard industrial cellular routers or gateways can cover all your needs. Does your router supplier provide customized R&D support?

4. What IoT solutions Bivocom have for you?

• Industrial cellular modems TD210, TW810

Both modem series provide you 1-RS232, 1-RS485, and it provides Modbus RTU/TCP/UDP protocol, MQTT*(TD210 only), built in independent industrial MCU. The main different is that TD210 is 4G LTE/3G/2G compliant, while TW810 is LTE CAT M1, NB-IoT, GPRS.

The industrial 4g modem TD210 and industrial LTE-M and NB-IoT TW810 have been widely used for automatic meter reading (AMR), especially for upgrading legacy meter to cloud, and serial port PLC controllers, IoT sensors.

• Industrial cellular routers TR321, TR341

Unlike the TD210, TW810, a MCU based cellular modem, the TR321, TR341 are an openwrt based Linux OS cellular routers that provides RS232, RS485, RJ45, which allows customers for installing their own Python or LUA based script. It has been used for IP camera, vending machine, ATM of bank, digital signage.

Industrial cellular routers TR321, TR341

• Industrial cellular gateways TG451, TG452, TG462S

Bivocom provides more interfaces and features than TR321, TR341, such as digital input, analog input*, relay output, USB*, the TG462S even provides a touch screen for local maintenance or data display on field. Besides, they support micro SD(option) or larger flash for local data storage and backup, and its edge computing capacity allows the data collect, process and analysis and storage at the edge network, its Modbus RTU to JSON send over MQTT protocol help to save the bandwidth for remote server.

Industrial cellular gateways TG451, TG452, TG462S

In conclusion, Bivocom has one-stop industrial cellular modems, routers and gateways for your choice, if you still couldn’t find the right solutions for your IoT project, please contact us to get answer from our expert.

The post How to choose the right industrial cellular routers or gateways for your IoT project? appeared first on Bivocom.

PLC is called a programmable controller. The PLC control system is a new generation of industrial control device that introduces microelectronics, computer, automatic control and communication skills on the basis of traditional sequence controllers. The purpose is to replace relays. , Execute logic, timekeeping, counting and other sequential control functions to establish a flexible long-distance control system.

The PLC industrial intelligent serial port gateway is suitable as the access node of large-scale distributed equipment. The embedded protocol analyzer can first collect the field device data through the protocol analysis to the gateway node for calculation and analysis, and then transmit it to the customer through the MQTT Internet of Things protocol Custom MQTT cloud channel.

PLC serial gateway function

1. industrial field devices remotely control;
2.  to achieve remote device firmware upgrade, download the program, the flexibility to access a variety of device management platform;
3.  industrial-site touch-screen remote control and remote configuration screen mapping;
4. at the same time Remote communication with multiple PLCs or touch screens;
5. protocol library rich, suitable for industrial site and remote data acquisition and transmission, remote maintenance and control equipment, large-scale industrial equipment lifecycle management, all types of communications protocol analysis and conversion of Things application scenarios.
6.  to achieve Siemens, Mitsubishi, Omron, Schneider, Delta, when Kymmene, and Lee, Panasonic, forever, for the sea and MODBUS series PLC and other mainstream hardware protocol parsing;
7.  to realize PLC remote monitoring, PLC remote programming, PLC remote debugging, PLC remote upload and download , PLC remote control, PLC data acquisition, PLC remote communication .

The post Industrial PLC serial gateway appeared first on Bivocom.

The rising concerns of climate change and air pollution concerns have called on the new technology to reduce the exhaust emission of the automobile and save our planet, which has driven the Electric Vehicle launched to the market and come to our life.

As we can see, the public EV charging stations or points have been built on roadside, shopping center, parking lot, etc., but how to remote monitor and manage the EV charging points has become a challenge to the EV charging point providers.

How to Reduce the Cost of Installing EV Charging Points by Using 4G LTE Router?

The Bivocom Industrial 4G LTE IoT Router TR341 has both wired and 4G LTE (Dual SIM) connectivity, while is flexible for providers to deploy their EV charging points, because they can choose either to use a 4G LTE or cable to provide the internet connectivity between onsite facilities and remote cloud server. What’s more, it supports auto switch between wired and 4G LTE, which means when SIM 1 is down, it will auto switch to SIM 2, while if both SIM are down, there is cable for final back, and this provides a reliable and robust connectivity.

And its rich I/O like RS232, RS485, ethernet port RJ45, as well as WIFI are flexible for diverse IIoT equipment, including IP camera, PLC, IPC, help the EV charging provider to remote monitor and manage their massive EV charging points.

Besides, the built-in WIFI of TR341 supports Radius client and Captive portal, which allows the operator onsite to manage and configure the cellular router in a convenient and secure way. While the captive portal is a great feature for WIFI advertisement when users access their WIFI network.

In addition, TR341 also supports built-in independent GPS module, easy to locate the position of EV charging points.

TR341 supports Modbus,JSON,MQTT protocols, so the onsite data can be calculated and transferred at the edge before sending to remote cloud server. which saves the cost of data transmission. TR341 also supports VPN (PPTP, L2TP, IPsec, GRE) for secure and private tunnel for connectivity.

Image: EV Charging Points at Parking Lots(TR341)

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While if you’re looking for an entry level industrial cellular router for your application, Bivocom also has a 2-LAN port 4G LTE IoT router-TR321, which has 1-RS232, 1-RS485, 2-RJ45, WIFI, and has most of the same features as TR341.

Image: EV Charging Points at Parking Building(TR321)

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What if the 4G coverage in your region is poor and not reliable?

As you may know, in some suburb areas and sites underground, 4G coverage maybe not that strong, while there is limit source for cable connectivity, what solution do we have?

No worry, there is another solution for you, LTE-M/NB-IoT Router TR321-M which provides global LTE CAT M1, NB-IoT and back support GPRS, as you may know, the coverage range of LTE CAT M1 and NB-IoT is much better than 4G LTE, what’s more, its data plan of IoT SIM card is also cheaper, so if your data transmission bandwidth requirement is not that big, the LTE-M/NB-IoT industrial cellular router TR321-M is a great solution for you.

In conclusion, Bivocom industrial cellular routers, such as TR341 and TR321 are great solutions for EV charging points and stations remote monitoring and management.

The post 4G and IoT Technology Empowers Smart EV Charging Stations appeared first on Bivocom.

LTE CAT M1 uses the existing LTE network to operate, but unlike NB-IoT (which uses unused spectrum or spectrum located in the guard band to operate) is that LTE CAT M1 operates in the same LTE as used in cellular applications Work within the frequency band. One of its advantages is that it has the ability to switch from one cell site to another, which makes it possible to use the technology in mobile applications; while NB-IoT does not allow mobile switching from one cell site to another cell site , So it can only be used for fixed applications, that is, applications limited to the area covered by a single cell site.

Since LTE Cat M1 technology can coexist with 2G, 3G and 4G mobile networks, it has all the advantages of mobile network security and privacy features, such as supporting user identity confidentiality, entity authentication, confidentiality, data integrity, and mobile devices Identification function, etc.

The latest LTE CAT M1 specification was approved in the 13th version of the 3GPP specification (LTE-Advanced Pro) in June 2016. According to the definition of Release 13, the technical specifications of LTE CAT M1 are as follows:

• Deployment: LTE frequency band in-band
• Downlink (downlink) peak data rate: 1 Mbps
• Uplink (uplink) peak data rate: 1 Mbps
• Delay time: 10-15 ms
• Technical bandwidth: 1.08MHz
• Duplex technology: full duplex or half duplex
• Transmit power level: 20/23 dBm

3GPP LPWAN standards

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In addition, NB-IoT focuses specifically on indoor coverage, low cost, long battery life, and high connection density. NB-IoT uses a subset of the LTE standard, but limits the bandwidth to a single narrow-band of 200kHz. It uses OFDM modulation for downlink communication and SC-FDMA for uplink communications.  IoT applications which require more frequent communications will be better served by NB-IoT, which has no duty cycle limitations operating on the licensed spectrum.

In March 2019, the Global Mobile Suppliers Association announced that over 100 operators have deployed/launched either NB-IoT or LTE-M networks.This number had risen to 142 deployed/launched networks by September 2019.

In conclusion, NB-Iot characteristics is: wide coverage, low power consumption, low cost, large connection and other characteristics.

  1. NB-iot network architecture

• Terminal: Mainly connect to the base station through the air interface. The terminal side mainly includes industry terminals and NB-IoT modules. Industry terminals include: chips, modules, sensor interfaces, terminals, etc.; NB-IoT modules include wireless transmission interfaces, soft SIM devices, sensor interfaces, etc.
• Wireless network side: includes two networking methods, one is Single RAN (Single Radio Access Network, integrated wireless access network), including 2G/3G/4G and NB-IoT wireless networks; the other is NB-IoT is newly built. It is mainly responsible for air interface access processing, cell management and other related functions, and connects to the IoT core network through the S1-lite interface, and forwards non-access layer data to higher-level network elements for processing.
• Core network side: Network elements include two networking modes, one is the integrated Evolved Packet C (Evolved Packet C data transmission mode, welcome to exchange and learn ore, EPC) network elements, including 2G/3G/4G Core network; the other is the core network of the Internet of Things. The core network side supports NB-IoT and eMTC user access through IoT EPC network elements and EPC shared by GSM, UITRAN, and LTE.
• IoT support platform: including HLR (Home Location Register), PCRF (Policy Control and Charging Rules Function), M2M (Machine to Machine, Internet of Things) platform.
• Application server: It is the final gathering point of IoT data, and performs data processing and other operations according to customer needs.

  2. NB-IoT application classification

  Above all, in the field of low-speed Internet of Things, NB-IoT, as a new standard, achieves the ultimate in cost, coverage, power consumption, and number of connections. This technology is widely used in eight typical industries, including public utilities, healthcare, smart cities, consumers, agricultural environments, logistics and warehousing, smart buildings, and manufacturing.

• Public utilities: meter reading (water/gas/electricity/heat), smart water (pipe network/leakage/quality inspection), smart fire extinguisher/fire hydrant.
• Manufacturing industry: production/equipment status monitoring, energy facilities/oil and gas monitoring, chemical park monitoring, large-scale rental equipment, predictive maintenance (home appliances, machinery, etc.).
• Medical and health: drug traceability, remote medical monitoring, blood pressure meter, blood glucose meter, heart guard monitoring.
• Smart city: smart street lights, smart parking, urban trash can management, public safety/alarm, construction site/urban water level monitoring.
• Logistics warehousing: asset/container tracking, warehouse management, fleet management/tracking, cold chain logistics (status/tracking).

• Smart buildings: access control, smart HVAC, smoke/fire detection, elevator failure/maintenance.
• Consumers: wearable devices, bicycle/moped anti-theft, smart luggage, VIP tracking (children/elderly/pet/vehicle rental), payment/POS machines.
• Agricultural environment: precision planting (environmental parameters: water/temperature/light/medicine/fertilizer), animal husbandry (health/tracking), aquaculture, food safety traceability, urban environmental monitoring (water pollution/noise/air quality PM2.5) .

The post A detailed description of the NB-IoT appeared first on Bivocom.

Configuration on Platform

1.To run up the MQTT feature, we need a MQTT Broker, here we take a broker account as example from CloudMQTT.com platform.

2.CloudMQTT.com also provide a simple websocket UI as a publisher for quick test. The Received messages will display respective Topic with Message from publishers.

Configuration on Bivocom Router

1.Bivocom Routers support serial communication (RS232 or RS485) via MQTT. Before go into setting, please connect your slave computer like PLC or sensors to RS232 /RS485 ports on Bivocom router.

2.Bivocom standard package contents Console Cable(3-Pin RS232), connect one side to RS232 ports on Bivocom router (the Black pin to GND port, while Brown pin to RX port, Blue pin to TX port). The other side connect to your slave computer, you may need extra adapter cable if your PLC/sensors don’t have standard serial communication interface.

3.Go into the WebUI of Bivocom router, >> Advanced>>Serial Communication, Enable Serial 485 or 232 >> Select MQTT as protocol.

4.Input the necessary MQTT server info we got from step 2, Save & Apply, if everything was correct, the Connection Status will indicate “CONNECTED”

5.On the CloudMQTT.com platform, you can also check the CONNECTIONS list the Bivocom router IP address on. After that, you are able to perform MQTT publisher on Bivocom router.

Feature Demo

1.To simulate the slave computer, we use a simple serial communication tool running on PC which connected to Bivocom router via RS232. Then send data as publisher to MQTT Broker.

2.MQTT server will receive the message with Topic we have set on Bivocom router.

3.To subscribe the data, we use a simple tool as subscriber.

• Connect the tool to MQTT server
• Set the exact subscribe Topic, it also support the variable parameter like “#” “+”
• On the data window, shows the received data from publisher accordingly.

The post Quick Setup MQTT On Bivocom Router appeared first on Bivocom.

Modbus is popular in industrial environments because it is openly published and royalty-free. It was developed for industrial applications, is relatively easy to deploy and maintain compared to other standards, and places few restrictions – other than the datagram (packet) size – on the format of the data to be transmitted.

The Modbus protocol uses character serial communication lines, Ethernet, or the Internet protocol suite as a transport layer.

Modbus supports communication to and from multiple devices connected to the same cable or Ethernet network. For example, there can be a device that measures temperature and another device to measure humidity connected to the same cable, both communicating measurements to the same computer.

Modbus is often used to connect a plant/system supervisory computer with a remote terminal unit (RTU) in Supervisory Control and Data Acquisition (SCADA) systems in the electric power industry. Many of the data types are named from industrial control of factory devices, such as Ladder logic because of its use in driving relays: A single physical output is called a coil, and a single physical input is called a discrete input or a contact.

Modbus has the following characteristics:

● The standard is open, users can use the Modbus protocol for free and with confidence, without paying license fees, and will not infringe on intellectual property rights.

● Modbus supports a variety of electrical interfaces, such as RS232, RS485, etc., and can also be transmitted on various media, such as twisted pair, optical fiber, wireless, etc.

● Modbus protocol frame format is simple, compact, easy to understand, easy for users to use, and easy for manufacturers to develop

Two transmission modes of MODBUS network

The controller can be set to any one of two transmission modes (ASCII or RTU) to communicate on a standard Modbus network. The user selects the desired mode, including serial communication parameters (baud rate, calibration mode, etc.). When configuring each controller, all devices on a Modbus network must select the same transmission mode and serial port parameters.

●ASCII mode

When the controller is set to communicate in ASCII (American Standard Code for Information Exchange) mode on the Modbus network, each 8Bit byte in the message is sent as an ASCII code (two hexadecimal characters). The main advantage of this method is that the time interval for sending characters can reach 1 second without error.

●RTU mode

When the controller is set to communicate in RTU (Remote Terminal Unit) mode on the Modbus network, each 8Bit byte in the message contains two 4Bit

Hexadecimal characters.

The main advantage of this method is: Under the same baud rate, more data can be transmitted than ASCII mode.

Modbus RTU information frame

Modbus information is transmitted in frames. Each frame has a definite start point and end point, so that the receiving device starts to read the address at the beginning of the message, and determines the device to be addressed and the end time of the information transmission.

The characters allowed to be sent in each area are hexadecimal 0-9, AF.

Devices on the network continuously monitor the information on the network, including the rest time. When receiving address data, each device immediately decodes it to determine whether it is its own address. After sending the next character number, there is also a static time of 3.5 characters before sending a new message. The entire message must be sent continuously. If there is a static time of more than 1.5 characters during the sending of frame information, the receiving device refreshes the incomplete information and assumes the next address data.

Address setting

The valid slave device address range is 0-247 (decimal), and the address range of each slave device is 1-247.

The host puts the address of the slave into the address area of ​​the message frame and addresses the slave. When the slave responds, put its own address into the address area of ​​the response message, so that the host can identify the slave address that has responded.

Address 0 is the broadcast address, which can be recognized by all slaves.

Function code setting

Commonly used function codes for Modbus:

The content of the data area

There are 2 hexadecimal data bits in the data area, and the data range is 00-FF (hexadecimal).

The information data sent by the master to the slave device contains the requested action specified in the function code of the master executed by the slave, such as the logical coil address, the number of processing objects, and the actual number of data bytes.

7 Error checking

The CRC field is two bytes, including a 16-bit value, and two 8-bit bytes, which are calculated by the transmission device and added to the message. The receiving device recalculates the receipt

Go to the CRC of the message and compare it with the value in the received CRC field. If the two values ​​are different, there is an error.

Modbus object types

The following is a table of object types provided by a Modbus slave device to a Modbus master device:

Object type	Access	Size	Address Space
Coil	Read-write	1 bit	00001 – 09999
Discrete input	Read-only	1 bit	10001 – 19999
Input register	Read-only	16 bits	30001 – 39999
Holding register	Read-write	16 bits	40001 – 49999

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