Description
MP3101S2 TRICONEX controller
MP3101S2 TRICONEX controller
Module Clips Drive controller servo motor
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What are the types of integrated IO modulesMP3101S2 TRICONEX controller
For a programmable logic controller, IO fulfills the responsibilities of data acquisition and instruction output. What control objectives can a PLC achieve, and the quantity and type of IO are crucial. For general integrated PLCs, the number and types of IO interfaces are constant. Some friends may ask, what if you encounter a complex control project with insufficient IO ports in the PLC? Don”t worry, nowadays PLCs have communication interfaces that can be connected to other IO couplers to achieve IO expansion. So, what are the types of IO modules that we can integrate in our daily lives? Actually, it can be mainly divided into four categories, namely:
1. Digital signal acquisition IO can achieve discontinuous signal acquisition, and a typical IO type is a counter input IO module.
Technology Oasis • Source: Guangcheng CAN Bus • Author: Guangcheng CAN Bus • 2022-05-09 09:52 • 1740 readings
For a programmable logic controller, IO fulfills the responsibilities of data acquisition and instruction output. What control objectives can a PLC achieve, and the quantity and type of IO are crucial. For general integrated PLCs, the number and types of IO interfaces are constant. Some friends may ask, what if you encounter a complex control project with insufficient IO ports in the PLC? Don”t worry, nowadays PLCs have communication interfaces that can be connected to other IO couplers to achieve IO expansion. So, what are the types of IO modules that we can integrate in our daily lives? Actually, it can be mainly divided into four categories, namely:
1. Digital signal acquisition IO can achieve discontinuous signal acquisition, and a typical IO type is a counter input IO module.
2. Digital output IO, which can send out command signals of digital quantities to control actuators, such as PWM IO, can send pulse signals to control servo motors and stepper motors. In addition to PWM IO, we often use relay output type IO.
3. After discussing digital IO, let”s talk about analog IO. Firstly, analog input IO includes voltage analog input IO, current analog input IO, temperature analog input IO, etc. They collect continuous signals.
4. Finally, there is the output type IO of analog quantity, mainly including voltage analog quantity output type IO and current analog quantity output type IO. Some friends may ask why there is no temperature this time, but there are relatively few applications, mainly based on voltage and current types.MP3101S2 TRICONEX controller
Industrial automation solutions, starting with remote IO modules!
The remote IO module is mainly used for collecting analog and digital signals on industrial sites, and can also output analog and digital signals to control equipment. It is possible to expand the input and output ports of data processing equipment such as PLCs and collection instruments. For example, a PLC only has 10 analog input interfaces, but if 30 analog quantities need to be collected on site, remote IO expansion needs to be added.
Furthermore, due to the distance between the equipment and the main control PLC or industrial computer, RS-485 bus is usually used for transmission. There are also some factories with high levels of automation that use industrial Ethernet to control remote IO modules. In the past, when laying lines between equipment and cabinets, people had to connect them one by one, which greatly increased the cost of cables and construction time. Moreover, if the distance was relatively long, they also faced problems such as voltage attenuation. And with the remote IO module, it effectively solves this problem. If your cabinet is 200 meters away from the site and you do not use remote IO, then you need to lay out each signal line for 200 meters. Installing the remote IO module on site can save you a lot of cable costs and reduce the complexity of construction from a cost perspective.
Simply put, sometimes some IO is set up in the on-site device cluster, which can be connected to the PLC through a communication cable to send the signal to any place where it is needed, saving wiring and PLC”s own IO points. Sometimes, the logical “remote” is because the allowed number of “local IO” cannot meet the actual needs, and it needs to be connected to the “remote IO template”, depending on the actual situation.
In addition, the general cabinet room is located on the device site. But some control signals, such as emergency stop and bypass, are implemented in the control room, so remote IO modules need to be used to send these signals to the control system in the cabinet room.
Why use remote I/O?
1. Because in some industrial applications, it is impossible to install PLCs with local I/O modules near on-site equipment due to harsh environments.
2. When you want to place the I/O module near the field device to eliminate long multi-core cables, you can receive signals from distant sensors and send remote control signals to control valves, motors, and other final actuators. The signal can be transmitted at any distance using various transmission protocols such as Ethernet and Profibus through high-speed media such as twisted pair and fiber optic.
3. Multiple transmission protocols such as Ethernet and Profibus can be used to send signals at any distance on high-speed media such as twisted pair and fiber optic.
The barium rhenium technology MXXT remote IO module uses industrial grade components with a wide working voltage of DC9-36V, which can operate normally within the range of -20~70 ℃. It supports RS485/232 communication mode, and the communication protocol adopts standard Modbus TCP protocol, Modbus RTU over TCP protocol, and MQTT protocol. We strive to fully meet the needs of our customers with an electrical and mechanical system that is anti-interference, resistant to harsh environments, and compatible with general use. It has stable performance, reliable quality, short delivery time, and fast response.
Advantages of Barium Rhenium Remote I/O Module
1. It can be controlled by remote commands.
2. Save the cost of using industrial control computers and IO cards, and Ethernet I/O modules can be directly connected to the upper computer system;
3. Replacing 4-20mA signal transmission with 10/100MHz Ethernet transmission has improved transmission speed;
4. Replacing various instrument controller signal lines with an Ethernet cable reduces the attenuation of remote signal transmission;
5. The signal cable of the instrument controller only needs to be connected to the Ethernet I/O module, greatly reducing cable costs and wiring workload.
6. Convenient installation method. Rail installation, high reliability, strong anti-interference ability, and more convenient on-site installation.
MQTT IoT Remote IO Module Based on Ethernet Communication Technology
MQTT IoT Remote IO Module Based on Ethernet Communication Technology
Barium rhenium technology remote IO modules are widely used in IoT scenarios such as intelligent transportation, smart water conservancy, smart agriculture, smart campuses, smart communities, smart power distribution, and smart water conservancy.
With the development of IIOT industrial Internet of Things technology, more and more traditional assets need to be connected to the internet, achieving unified data collection and analysis, and breaking the phenomenon of traditional device information silos. The barium rhenium technology remote IO module M160T, which supports IoT protocols, has become an excellent choice for many enterprises to achieve device networking, remote control, and data collection based on the compatibility of existing devices and the accessibility of IoT platforms!
Ethernet communication technology is a mature communication technology because it has the characteristics of stability, reliability, mature technology, fast transmission speed, and fast construction wiring. Due to its wide application, Ethernet communication through the MQTT protocol is the main way for enterprise equipment to go to the cloud. Barium rhenium technology can quickly collect data and control such as air compressor room, property living pump room, street light control, liquid level collection, temperature and humidity collection through Ethernet remote IO module.MP3101S2 TRICONEX controller
So, why is the remote IO module of barium rhenium technology widely used in the field of industrial IoT? The specific reasons are as follows.
1. Actively connect to cloud platforms:
Based on the characteristics of Ethernet communication networks, the barium rhenium technology remote IO module does not require complex settings such as peanut shells to achieve the Internet of Things. The barium rhenium technology remote IO module needs to support both TCP client and TCP server functions.
2. Compatibility with existing systems:
It supports TCP Server and Modbus TCP protocol functions, and is compatible with device access of traditional upper level systems or HMI TCP clients.
3. Support multiple IoT platforms:
Supports standard MQTT, Modbus TCP, and Modbus RTU over TCP protocols. It can be connected to public cloud IoT platforms and user built MQTT private clouds through the MQTT protocol. It can also be connected to SCADA and DCS systems through Modbus TCP.
4. Rich IO interfaces and scalability:
There are many types of IO for industrial field data collection and replication. The Ethernet IO module of barium rhenium technology supports signal acquisition from various devices such as 4-20Ma, 0-20mA, 0-5V, 0-10V, RS485, DI, DO, PT100, PT1000, pulse input, pulse output, etc. At the same time, it expands the instrument data reading ability of RS485 devices.
5. Convenient installation method:
The volume of industrial on-site control boxes is often very limited, and the barium rhenium technology Ethernet IO module adopts a direct plug-in connection terminal and rail installation method. The compact volume greatly saves space in the control box!
6. Industrial grade design
The industrial environment is harsh, and the remote IO module using barium rhenium technology needs to adopt an industrial grade design, which can work continuously and stably in harsh environments.
Through the use of barium rhenium technology remote IO modules, there is no need to replace existing various enterprise assets, and the digital transition to the Internet of Things platform can be quickly achieved. Therefore, barium rhenium technology remote IO modules are widely used in industrial IoT, such as intelligent real estate, intelligent campus, intelligent factory, intelligent transportation, intelligent water conservancy, intelligent agriculture, intelligent campus, intelligent community, intelligent transportation, and many other industries.
What is the role of distributed IO modules and what are their main applications in
The distributed IO module transmits status signals from the measurement and control field to various measurement and control fields for control. It is mainly used in the industrial field and can also be used for detection of equipment such as air conditioners and motors.
In distributed systems, there are important business data closely related to system operation, as well as data related to nodes, application services, and data services, which are crucial for the normal operation of clusters.
IO on general PLCs is usually closely followed by CPU units, but in order to facilitate connection and maintenance, the concept of distributed IO has been proposed in the industrial field. That is to say, the IO unit can be arranged far away from the PLC CPU unit and communicate through the network communication protocol of the device layer.
The distributed IO module is developed for detecting and implementing remote control of various types of standard analog and switch signals (frequency, pulse, or switch state signals) in the field of measurement and control. The series of modules can digitize the test signal front-end and transmit it to the host through optical fiber; Or transmit the control instructions sent by the host to the controlled device to achieve remote control. Especially suitable for state detection and control of complex electromagnetic environments in power, industrial control, on-site switchgear, and large power equipment.
The role of distributed IO modules:
1. Support 4-way switch digital quantity
2. Supports 8 analog inputs
3. 4 relay outputs, 1 RS485 serial port data acquisition to Ethernet
4. 485 to Ethernet serial server
5. Supports Modbus to TCP/UDP protocol conversion
6. Supports virtual serial ports and interfaces with various configuration software
7. Support 0-5V, 0-10V, 0-30V range acquisition
8. Supports 0-20ma and 4-20ma range acquisition
What are the characteristics of a demonstration system based on IO Link slave stations
IO Link is an industrial communication interface that is independent of any fieldbus and suitable for simple sensors and actuators at the lowest level of industrial control. The IO Link system includes IO Link devices (such as sensors and actuators), IO Link master stations, and cables for standard sensors. The system structure is shown in Figure 1. For example, when a remote IO module compatible with EtherNet/IP serves as the master station, in addition to standard I/O signals, the module sends and receives configuration data, diagnostic data, or enhanced process data through a pulse modulation process, which is then packaged into EtherNet/IP data packets and finally transmitted to the network master station, usually a PLC. In the above applications, the connection between remote I/O and IO Link devices remains the same as that of traditional discrete devices. The advantage of IO Link mainly lies in its greater information exchange capability, which was previously impossible to achieve with standard I/O devices. Another advantage of IO Link is that it does not rely on any fieldbus, and through any I/O module that complies with the IO Link protocol (including local I/O and remote I/O), IO Link sensors or actuators can be integrated into any fieldbus system.
In order to further study the architecture, communication mechanism, and development application of the IO Link system, an IO Link slave toolkit can be designed and developed, including a universal development module for IO Link, an IO Link analysis tool, and an IO Link slave protocol stack. The IO Link universal development module is the foundation for this work and also serves as a bridge between the IO Link master station and equipment signals. The IO Link analysis tool can help developers and testers analyze communication details to identify and solve problems. The IO Link slave protocol stack is a firmware library that provides a hardware abstraction layer and application program interface, allowing developers to easily and quickly develop IO Link slave products on various microprocessor platforms. The IO Link slave station studied in this article only focuses on digital (button) signal input and digital signal output (indicator light). The design of the IO Link universal development module only needs to be expanded on this basis to have the ability to process analog signals.
The IO Link Master module used in this article, USB IO Link Master, can connect IO Link devices to a PC, which can be configured and tested through the IO Link Device Tool software or demonstrated device functionality. IO Link devices must be described through a device description file (IODD file), which includes a set of XML text files and PNG graphic files, which contain information about device identification, communication characteristics, parameters, process data, and diagnostic data. The portion within the elliptical dashed line in Figure 2 is an IO Link three wire cable, with L+/I – being a 24 V DC power supply and C/Q being a signal line used to transmit process data, diagnostic data, configuration data, etc. The IO Link universal development module is mainly composed of data transceivers and microprocessors. It can process input signals from sensors and transmit information to the IO Link master station. It can also receive and process data information from the master station and transmit it to the actuator. The IO Link analysis tool can help developers view, record, analyze data, and understand communication details. This part of the design is not discussed in this article.
Introduction to IO Link Communication ModeMP3101S2 TRICONEX controller
IO Link devices can operate in SIO mode (standard I/O mode) or IO Link mode (communication mode). After power on, the device always operates in SIO mode. The port of the main station has different configuration methods. If configured in SIO mode, the main station considers the port as a standard digital input. If configured in communication mode, the main station will automatically identify the communicable devices for communication.
2.1 Data TypesMP3101S2 TRICONEX controller
The three basic data types for IO Link communication are periodic data (or process data PD), non periodic data (or service data SD), and event.
The process data (PD) of the device is transmitted periodically in the form of a data frame, while service data (SD) is only exchanged after the master station issues a request. Figure 3 shows a typical IO Link message structure. When an event occurs, the “event flag” of the device is set, and the main station reads the reported event (service data cannot be exchanged during the reading process) upon detecting the setting. Therefore, events such as pollution, overheating, short circuits, or device status can be transmitted to the PLC or visualization software through the main station
2.2 Parameter data exchange
Since service data (SD) must be transmitted through PLC requests, SPDU (Service Protocol Data Unit) is defined. In the main station, requests for read and write services are written to SPDU and transmitted to devices through the IO Link interface.
The general structure of SPDU is shown in Figure 4, and its arrangement order is consistent with the transmission order. The elements in SPDU can take different forms depending on the type of service. SPDU allows access to data objects that are intended for transmission, while Index is used to specify the address of the requested data object on the remote IO Link device. In IO Link, there is a term called direct parameter page, which stores parameter information such as minimum cycle time, supplier ID, and master station commands. The data objects accessible in the direct parameter page can be selectively provided through SPDU.
HMT7742 is an IO Link slave transceiver chip that serves as a bridge between the MCU of external sensors or actuators and the 24V signal line that supports IO Link communication. When the IO Link device is connected to the master station, the master station initializes communication and exchanges data with the MCU. HMT7742 serves as the physical layer for communication.
Due to the fact that the three indicator lights (rated voltage 24 V) controlled by the output port of the MCU are powered by the IO Link power cord, it is necessary to monitor the current on the power cord in order to trigger appropriate corrective measures when the current exceeds a set threshold, such as removing the indicator lights from the IO Link power cord. The current monitoring module uses an INA194 current detection amplifier. As a high detection current detector, INA194 is directly connected to the power supply and can detect all downstream faults. It has a very high common mode rejection ratio, as well as a large bandwidth and response speed. It can amplify the voltage on the induction resistor 5O times and output it to the forward input terminal AIN0 of the MCU internal voltage comparator. When the voltage value of AIN0 exceeds the threshold set at the reverse input terminal, By controlling the low level output of PB0, the indicator LAMP can be cut off from the IO Link power line to achieve overcurrent protection function. This part of the circuit is shown in Figure 6.
Application Scheme of Industrial Ethernet Remote IO Module in Intelligent Manufacturing Workshop
With the advent of Industry 4.0, intelligent manufacturing has become a trend in industrial production. Intelligent manufacturing requires efficient, stable, and reliable industrial Ethernet remote IO modules to monitor the production process. This article will share an application case of an intelligent manufacturing workshop based on industrial Ethernet remote IO module.MP3101S2 TRICONEX controller
The production process of this intelligent manufacturing workshop is mainly divided into two parts: injection molding and automated assembly. The injection molding process requires controlling parameters such as the melting temperature of the melt, the speed and pressure of the injection molding machine. The automated assembly process requires controlling the actions of the assembly robot and detecting the quality of the product. In addition to these production process data, there are also equipment production data such as daily and weekly production in the workshop, as well as equipment status data such as operation, manual, automatic, mold adjustment, and alarm.
In the past, the production process of the factory mainly relied on traditional hard wiring to control the production process, resulting in low work efficiency due to the need for frequent replacement of transmission lines to meet production needs. Moreover, it is very difficult to collect a large number of types of detection and monitoring data for intelligent manufacturing. In order to improve efficiency, production quality, and reliability, the factory has introduced the industrial Ethernet remote IO module MxxT using barium rhenium technology.
The injection molding machine itself comes with MODBUS industrial control bus data or basic status signal output. The barium rhenium technology remote IO module collects data from the device interface RS232/RS485 port, collects status information of the injection molding machine such as startup, operation, and pause, and uploads it to the injection molding machine controller, or wirelessly uploads it to the cloud server. Based on devices, according to the communication protocols and interfaces of different devices, data is obtained by calling their interface channels, and then transmitted to the server.
The remote IO module is connected to the controller of the injection molding machine, and the operation data of the injection molding machine is uploaded and distributed wirelessly, achieving remote monitoring and intelligent control of the injection molding machine. In addition, the remote I/O module supports perceptual access to peripheral devices such as mold temperature machines, cutting machines, and dryers for injection molding machines, providing users with smart factory services.
During the injection molding process, the industrial Ethernet remote IO module transmits real-MP3101S2 TRICONEX controllertime data such as temperature, pressure, and speed to the main controller for monitoring and adjustment, ensuring the stability and compliance of production parameters under different conditions. In the automated assembly process, the industrial Ethernet remote IO module collects data through sensors and other devices, and transmits the relevant data to the main controller for adjustment of relevant actions. For example, the industrial Ethernet remote IO module can monitor the actions of assembly robots, detect the accuracy of product assembly and product quality, and ensure the production quality and stability of the product. At the same time, all production data can also be collected and analyzed remotely, helping enterprise managers better monitor production efficiency and quality.
By introducing industrial Ethernet remote IO modules, this intelligent manufacturing workshop not only improves production efficiency and stability, but also reduces labor and energy costs. Because the industrial Ethernet remote IO module can help enterprises complete the collection and monitoring of production data with one click, as well as avoid unnecessary line replacement and the need for workers to enter and exit the production process, thereby reducing costs and improving production efficiency for enterprises.
In summary, the application of industrial Ethernet remote IO modules in intelligent manufacturing workshops not only improves production efficiency and quality, reduces costs, but also achieves intelligent and digital management of production processes, bringing more opportunities and development space for enterprise development.
In addition, this device is widely used for networking and data collection of industrial equipment such as injection molding machines, air compressors, CNC machine tools, on-site PLCs, instruments, sensors, CNC, and electromechanical equipment.
Building a High Channel Density Digital IO Module for the Next Generation Industrial Automation Controller
There are currently many articles introducing Industry 4.0, and smart sensors are becoming increasingly popular in factory environments (I and other authors have written about these topics). Although we have all noticed a significant increase in the use of sensors in factories, processing plants, and even some newly built automation systems, the widespread use of sensors has also brought about an important change, which is the need to handle a large amount of IO within these old controllers. These IOs may be digital or analog. This requires the construction of high-density IO modules with size and heat limitations. In this article, I will focus on digital IO, and in subsequent articles, I will introduce analog IO.
Usually, digital IO in PLC consists of discrete devices such as resistors/capacitors or independent FET drives. In order to minimize the size of the controller as much as possible and to handle 2 to 4 times the number of channels, this has led to a shift from a separate approach to an integrated approach.
We can use the entire article to illustrate the drawbacks of the split method, especially when the number of channels processed by each module reaches 8 or more. However, when it comes to high heat/power consumption, a large number of split components (from the perspective of size and mean time between failures (MTBF)), and the need for reliable system specifications, it is sufficient to demonstrate that the split method is not feasible.
Figure 1 shows the technical challenges faced in building high-density digital input (DI) and digital output (DO) modules. In both Di and DO systems, size and heat dissipation issues need to be considered.
Digital input
size
heat
Supports all input types
Type 1, 2, 3, Input
Supports 24 V and 48 V inputs
Robust operating specifications
Wire breakage detection
Digital output
Support for different types of output driver configurations
size
Integrated demagnetization of inductive loads
Heat – When driving multiple outputs
Drive accuracy
diagnosis
For digital input, it is also important to note that it supports different input types, including 1/2/3 type inputs, and in some cases, 24V and 48V inputs. In all cases, reliable operating characteristics are crucial, and sometimes circuit detection is also crucial.
For digital outputs, the system uses different FET configurations to drive the load. The accuracy of the driving current is usually an important consideration. In many cases, diagnosis is also very important.
We will explore how integrated solutions can help address some of these challenges.
Design a High Channel Density Digital Input Module
The traditional split design uses a resistive voltage divider network to convert 24V/48V signals into signals that can be used by microcontrollers. The front-end can also use discrete RC filters. If isolation is required, external optocouplers are sometimes used.
Figure 1 shows a typical discrete method for constructing digital input circuits.
Figure 1. Considerations for digital input and output modules.
This type of design is suitable for a certain number of digital inputs; 4 to 8 per board. Beyond this number, this design will soon become impractical. This separation scheme can bring various problems, including:
High power consumption and related board high temperature points.
Each channel requires an optocoupler.
Excessive components can lead to low FIT rate and even require larger devices.
More importantly, the split design method means that the input current increases linearly with the input voltage. Assuming a 2.2K Ω input resistor and 24V V is used. When the input is 1, for example, at 24V, the input current is 11mA, which is equivalent to a power consumption of 264mW. The power consumption of the 8-channel module is greater than 2W, and the power consumption of the 32-bit module is greater than 8W. Refer to Figure 3 below
From a cooling perspective alone, this split design cannot support multiple channels on a single board.
One of the biggest advantages of integrated digital input design is the significant reduction in power consumption, thereby reducing heat dissipation. Most integrated digital input devices allow configurable input current limitations to significantly reduce power consumption.
When the current limiting value is set to 2.6mA, the power consumption is significantly reduced, with each channel approximately 60mW. The rated value of the 8-channel digital input module can now be set below 0.5
Another reason for opposing the use of split logic design is that sometimes DI modules must support different types of inputs. The standard 24V digital input specifications published by IEC are divided into Type 1, Type 2, and Type 3. Type 1 and Type 3 are usually used in combination because their current and threshold limits are very similar. Type 2 has a current limit of 6mA, which is higher. When using the split method, it may be necessary to redesign as most discrete values need to be updated.
However, integrated digital input products typically support all three types. Essentially, Type 1 and Type 3 are generally supported by integrated digital input devices. However, in order to meet the minimum current requirement of 6mA for Type 2 input, we need to use two channels in parallel for one field input. And only adjust the current limiting resistance. This requires a circuit board change, but the change is minimal.
Modify the watchdog time of the PROFINET IO device under 16 STEP7
3.2 Check if the installation of PROFINET IO communication equipment meets the specifications
Most cases of PROFINET IO communication interference problems are caused by equipment installation that does not comply with the installation specifications for PROFINET IO communication, such as incomplete shielding, unreliable grounding, and being too close to interference sources. Installation that meets the specifications can avoid communication failures caused by electromagnetic interference. You can refer to the following brief installation requirements for PROFINET:
1. Wiring of PROFINET MP3101S2 TRICONEX controller
In order to reduce the coupling of electric and magnetic fields, the larger the parallel distance between PROFINET and other power cable interference sources, the better. In accordance with IEC 61918, the minimum distance between PROFINET shielded cables and other cables can be referred to Table 1. PROFINET MP3101S2 TRICONEX controller can be wired together with other data cables, network cables, and shielded analog cables. If it is an unshielded power cable, the minimum distance is 200mm.
Comprehensive analysis of the principle and application skills of microcontroller IO port
IO port operation is the most basic and important knowledge in microcontroller practice. This article takes a long time to introduce the principles of IO ports. I also consulted a lot of materials to ensure the accuracy of the content, and spent a long time writing it. The principle of IO ports originally required a lot of in-depth knowledge, but here it has been simplified as much as possible for easy understanding. This will be of great help in solving various IO port related problems in the future.
The IO port equivalent model is my original method, which can effectively reduce the difficulty of understanding the internal structure of the IO port. And after consulting and confirming, this model is basically consistent with the actual working principle.
I mentioned a lot earlier, and many people may already be eager to actually operate microcontrollers. The IO port, as the main means of communication between the microcontroller and the outside world, is the most basic and important knowledge for microcontroller learning. Previously, we programmed and implemented an experiment to light up the LED at the IO port. This article will continue to introduce the relevant knowledge of the IO port.
In order to better learn the operation of IO ports, it is necessary to understand the internal structure and related concepts of IO ports. These knowledge are very helpful for subsequent learning, with a focus on understanding and no need to memorize them intentionally. If you don”t remember, just come back and take a look. If you use it too much, you will naturally remember.
We have said that the most accurate and effective way to understand a chip is to refer to official chip manuals and other materials. But for beginners of microcontrollers, it may be difficult to understand the chip manual directly, especially when they see a bunch of English, unfamiliar circuits, and terminology. If it were me, I would definitely be crazy. But here I still provide a picture taken from Atmel”s official “Atmel 8051 Microcontrollers Hardware Manual”.
The purpose of giving this picture is not to dampen everyone”s enthusiasm for learning, but to help everyone understand how the various microcontroller materials we have seen come from and whether they are accurate. All of these can be clarified through official information, which will be helpful for everyone to further learn something in the future.
Introduction to the Second Function
The above figure is the authoritative 51 microcontroller IO port structure diagram provided by the official. It can be seen that the internal structure of the four sets of IO ports of the microcontroller is different, because some IO ports have a secondary function, as mentioned in the introductory section.
Do you remember this pin diagram? The second function name of the IO port is marked in parentheses. Except for P1, each interface has a second function. When introducing the microcontroller system module, I mentioned that the 51 microcontroller has an interface for reserved extended memory, which is the second function of P0 and P1 in the figure (while also using pins such as 29 and 30). Because it is not widely used and involves in-depth knowledge, no specific research will be conducted. By the way, the AD0~AD7 we see here are actually used for parallel ports. The second function of the P3 port, including serial port, will be introduced in detail later.
The drawbacks of network IO and the advantages of multiplexing IO
In order to talk about multiplexing, of course, we still need to follow the trend and adopt a whiplash approach. First, we will talk about the drawbacks of traditional network IO and use the pull and step method to grasp the advantages of multiplexing IO.
For the convenience of understanding, all the following code is pseudo code, and it is sufficient to know the meaning it expresses.
Blocking IO
The server wrote the following code to handle the data of client connections and requests.
Listenfd=socket()// Open a network communication port
Bind (listenfd)// binding
Listen (listenfd)// Listening while (1){
Connfd=accept (listenfd)// Blocking connection establishment
Int n=read (connfd, buf)// Blocking read data
DoSomeThing (buf)// What to do with the data you read
Close (connfd)// Close the connection and wait for the next connection in a loop
}
This code will be executed with stumbling blocks, just like this.
It can be seen that the thread on the server is blocked in two places, one is the accept function and the other is the read function.
If we expand on the details of the read function again, we will find that it is blocked in two stages.
This is traditional blocking IO.
The overall process is shown in the following figure.
So, if the client of this connection continues to not send data, the server thread will continue to block on the read function and not return, nor will it be able to accept other client connections.
This is definitely not feasible.
Non blocking IO
To solve the above problem, the key is to modify the read function.
A clever approach is to create a new process or thread every time, call the read function, and perform business processing.
While (1){
Connfd=accept (listenfd)// Blocking connection establishment
Pthread_ Create (doWork)// Create a new thread
}
Void doWork(){
Int n=read (connfd, buf)// Blocking read data
DoSomeThing (buf)// What to do with the data you read
Close (connfd)// Close the connection and wait for the next connection in a loop
}
In this way, once a connection is established for a client, it can immediately wait for a new client connection without blocking the read request from the original client.
However, this is not called non blocking IO, it just uses multithreading to prevent the main thread from getting stuck in the read function and not going down. The read function provided by the operating system is still blocked.
So true non blocking IO cannot be achieved through our user layer tricks, but rather by imploring the operating system to provide us with a non blocking read function.
The effect of this read function is to immediately return an error value (-1) when no data arrives (reaches the network card and is copied to the kernel buffer), rather than waiting for blocking.
The operating system provides this feature by simply setting the file descriptor to non blocking before calling read.
Fcntl (connfd, F_SETFL, O_NONBLOCK);
Int n=read (connfd, buffer)= SUCCESS;
In this way, the user thread needs to loop through the call to read until the return value is not -1, and then start processing the business.
We noticed a detail here.
Non blocking read refers to the stage where data is non blocking before it reaches the network card, or before it reaches the network card but has not been copied to the kernel buffer.
When the data has reached the kernel buffer, calling the read function is still blocked and requires waiting for the data to be copied from the kernel buffer to the user buffer before returning.
The overall process is shown in the following figure
IO multiplexing
Creating a thread for each client can easily deplete the thread resources on the server side.
Of course, there is also a clever solution. After accepting each client connection, we can put the file descriptor (connfd) into an array.
Fdlist. add (connfd);
Then create a new thread to continuously traverse the array and call the non blocking read method for each element.
While (1){
For (fd “- fdlist){
If (read (fd)!=- 1){
DoSomeThing();
}
}
}
In this way, we successfully processed multiple client connections with one thread.
Do you think this means some multiplexing?
But this is just like using multithreading to transform blocked IO into seemingly non blocking IO. This traversal method is just a small trick that our users have come up with, and every time we encounter a read that returns -1, it is still a system call that wastes resources.
Making system calls in a while loop is not cost-effective, just like making rpc requests while working on distributed projects.
So, we still need to plead with the operating system boss to provide us with a function that has such an effect. We will pass a batch of file descriptors to the kernel through a system call, and the kernel layer will traverse them to truly solve this problem.
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