I/O Interface Concept
I/O interface is an electronic circuit (in the form of IC chip or interface board), which is composed of a number of specialized registers and corresponding control logic circuits. It is the medium and bridge for exchanging information between CPU and I/O devices, and the connection and data exchange between CPU and external devices and memory need to be realized through the interface device, which is known as I/O interface, and the latter is known as memory interface. Memory is usually synchronized under the control of the CPU, the interface circuit is relatively simple; and I / O device variety, the corresponding interface circuit is also different, therefore, it is customary to say that the interface only refers to the I / O interface.
I/O Interface Basic Functions
(1) Perform port address decoding device selection.
(2) Provide I/O device status information and command decoding to the CPU.
(3) Timing and corresponding timing control.
(4) Provides buffering of transmitted data to eliminate differences in "timing" or data processing speed between the computer and peripherals.
(5) Providing compatibility transformations between the computer and peripheral devices with respect to information formats. Provide electrical adaptations.
(6) It can also realize the exchange of information between CPU and peripheral devices by interrupting.
Control method
(1) Program query method
In this method, the CPU asks the current state of the specified peripheral through I/O instructions, and if the peripheral is ready, it carries out the input or output of data; otherwise, the CPU waits and queries cyclically.
The advantage of this method is that the structure is simple, only a small number of hardware circuits can be, the disadvantage is that the speed of the CPU is much higher than the peripheral, so usually in a waiting state, the work efficiency is very low.
(2) Interrupt processing method
In this way, the CPU is no longer passive waiting, but can execute other programs, once the peripheral is ready for data exchange, it can put forward a service request to the CPU, if the CPU responds to the request, it will temporarily stop the execution of the current program, go to the execution of the service program corresponding to the request, and then continue the execution of the program that has been interrupted after the completion of the original program.
The advantages of interrupt processing are obvious, it not only saves the CPU from querying the status of the peripheral and waiting for the peripheral to be ready to spend time to improve the efficiency of the CPU, but also to meet the real-time requirements of the peripheral. However, it is necessary to assign an interrupt request number and corresponding interrupt service program for each I/O device, and in addition, an interrupt controller (I/O interface chip) is needed to manage the interrupt requests made by the I/O device, such as setting the interrupt mask, interrupt request priority, and so on.
In addition, the disadvantage of the interrupt processing method is that every transmission of a character must be interrupted to start the interrupt controller, but also to retain and restore the scene in order to continue the execution of the original program, the workload is very large, so that if a large number of data exchanges are required, the performance of the system will be very low.
(3) DMA (Direct Memory Access) transfer method
One of the most obvious features of DMA is that it does not use software but a specialized controller to control the exchange of data between the memory and peripherals, without the intervention of the CPU, greatly improving the efficiency of the CPU.
Before DMA data transfer, the DMA controller applies for bus control to the CPU, and the CPU hands over the control if it is allowed to do so. Therefore, the bus control is held by the DMA controller during data exchange, and at the end of the transfer, the DMA controller hands the bus control back to the CPU.
(4) Unconditional transfer method
(5) I/O channel method
(6) I/O processor method
Industrial ControlNetworks
Industrial control networks are generally local area networks (LANs), which generally function within a range of a few kilometers. It connects measurement and control devices distributed around production facilities into automation systems with different functions. Control networks are found in production plants, assembly lines, greenhouses, grain depots, dams, tunnels, various traffic control systems, buildings, the military, firefighting, environmental testing, buildings and homes.
Nodes of industrial control networks
The nodes of an industrial control network are mostly measurement devices with computing and communication capabilities. They may have an embedded CPU, but the function is relatively single, its computing power may be far less than an ordinary PC, there is no keyboard, display and other human-computer interaction interfaces. Some even do not have a CPU, microcontroller, only with a simple communication interface, such as limit switches, inductive switches and other types of switches, photoelectric, temperature, pressure, flow, level and other types of sensors, transmitters, a variety of data acquisition devices and so on.
Control network tasks and working environment
Industrial control network to face the industrial production of strong electromagnetic interference, facing a variety of mechanical vibration, facing the cold and hot field work environment, to go to the control network can adapt to this harsh working environment. In addition, self-control equipment varies greatly, the realization of the control network interconnection and interoperability is often very difficult.
Control network of real-time requirements
Control network must meet the real-time control requirements. Real-time control of certain variables of the data often require accurate and regular refreshment, the control role must be completed within a certain time limit, or related control actions must be completed in accordance with the sequence of matters specified.
Field interface classification
Based on these characteristics of the control network, a variety of interfaces must ensure that meet the requirements of the control network. At present, there are four types of interfaces in the industrial field:
(1) Platform Relevance Common Protocol: OPC / DDE
OPC is proposed for the purpose of standardizing the software interfaces between devices and applications from different supplying vendors and making the exchange of data between them simpler. As a result, it is possible to provide users with process control software components that can be freely combined and used without relying on a specific development language and development environment.
(2) Platform-independent communication protocols: ModBus, ProfiBus
The Modbus protocol is a universal language used in electronic controllers. Through this protocol, controllers communicate with each other, controllers through the network (e.g. Ethernet ) and other devices. It has become a common industrial standard. Profibus, an international, open, manufacturer-independent fieldbus standard, allows control devices from different manufacturers to be connected to an industrial network for centralized monitoring and control. Profibus transmission speed can be selected from 9.6kbaud to 12Mbaud and all devices connected to the bus should be set to the same speed when the bus system is activated. Widely used in manufacturing automation, process industry automation and building, transportation and power and other areas of automation. profibus is a fieldbus technology for factory automation shop floor level monitoring and field device level data communication and control.
(3) Platform-independent proprietary protocols: most DCS protocols, industrial Ethernet protocols
(4) Special protocols: Programming port, print port and other special ways to obtain the agreement
Industrial transmission communication protocols are more varied mainly due to historical legacy and artificial monopoly. Although there are still a large number of fieldbus standards, but no standard is more vital than industrial Ethernet.
Summary of various fieldbuses/protocols/interfaces
Name of the industrial automation bus/protocol/interface Identification Characteristics Introduction Description
ASI Sensor/actuator bus for the lower control level AS-interface is used to connect sensors and actuators to the upper control level with simple and economical wiring. the AS interface complies with the international standards EN 50295 and IEC 62026-2. AS-Interface (AS-i = Actuator/Sensor Interface) is a fieldbus communication scheme for connecting actuators and sensors. Organizer] ASI interfaces/protocols/specifications
BACnet== Building Automation Control Network Data Communication Protocol Building Automation Control Network 【Organize】 Industrial Automation of Building Automation Communication Protocol: BACnet
CANopen Multi-master bus for actuators/sensors Effective use of the bus bandwidth allows CANopen to achieve short system response times at relatively low data rates. the main advantages of the CAN bus are: high data security and the ability to retain the multi-master capability.
CC-Link Fieldbus for the Asian market CC-Link (Control & Communication Link) is an open bus system for communication between the control level and the fieldbus level, mainly in the Asian region.
ControlNet Standardized Fieldbus ControlNet is an open standard fieldbus system. The bus protocol allows cyclic and acyclic data to be exchanged over the bus at the same time without interfering with each other.
DALI Communication standard for building automation The DALI standard (IEC 60929) is a manufacturer-spanning protocol that aims to ensure the interoperability of electronic ballasts in lighting applications. This new standard is used to replace the 1-10V dimmer interface. Digital AddressableLighting Interface (DALI) is a building automation standard for the digital control of electronic ballasts. DALI is used as a subsystem, e.g. for lighting, blinds or temperature control, and communicates directly with the building management system. Industrial Automation Bus for Building Automation - Lighting Interface: DALI
DeviceNet Device bus with CAN technology DeviceNet is a sensor/actuator bus system that originated in the USA, but is now increasingly used in Europe and Asia. deviceNet is based on the CAN (Controller Area Net) bus.
DMX EIB The communication standard in the field of building automation EIB (European Installation Bus) is a bus system for building wiring, which is widely used mainly in Europe.
EnOcean is a maintenance-free, battery-free and wire-free wireless technology. It is mainly used in building automation: different device modules (e.g. a light switch) are embedded with EnOcean support. Then the device can be controlled by the controller. Industrial Automation of Building Automation Wireless Protocol: EnOcean
EtherCAT== High-speed real-time Ethernet fieldbus EtherCAT ( Ethernet Control Automation Technology ) is an Ethernet solution for industrial automation characterized by high performance and easy operation.
EtherNet/IP Industrial Ethernet solutions from ODVA Ethernet/IP is the industrial Ethernet standard developed by ODVA (Open DeviceNet Vendor Association) and is based on the Ethernet TCP/IP and UDP/IP standards.
Ethernet TCP/IP Network Bus Ethernet is an important standard in the office sector. Many of the advantages of Ethernet, such as high transmission rates, simple integration into existing networks, a wide range of services, and a wide variety of interfaces, are also reflected in the Ethernet products from Beckhoff.
FIAS FIAS==Fidelio Interface and Application Specification== (Estimated) **F**idelio **I**nterface **A**pplication **S**pecification FIAS (Fidelio Interface and Application Specification) is the world's leading interface to hospitality management software. Organizer] Industrial automation of building automation of hotel management software interface: FIAS and Fidelio
Fipio WorldFIP-compliant fieldbus FIP complies with the European standard EN 50170 and is supported by independent manufacturers from the WorldFIP fieldbus organization. The bus performance can be adapted to the specific application through the exchange of cyclic and non-cyclic variables and information.
IEEE 1588 InterBus Interbus, introduced to the market in 1987 Interbus fieldbuses are characterized by easy configuration, high speed and reliability. This master/slave system shift register communication protocol can improve the efficiency of cyclic communication.
[Organizer] Fieldbus: InterBus
IO-Link IO-Link perfectly standardizes the different interfaces required for control systems and tool processing. iO-Link allows sensors and actuators to be connected to the control layer using an economical point-to-point connection method. As an open interface, IO-Link can be integrated into all commonly used fieldbus systems. an IO-Link system consists of IO-Link devices such as sensors, actuators or a combination of both. They use the traditional three-wire connection technology. Organizer] IO-Link
LightBus== High-speed fiber-optic fieldbus Interference-free fieldbus communication for high-speed machine control This is a fiber-optic bus system developed by Beckhoff with a high degree of maturity, the main features include: high immunity to electromagnetic interference, easy installation, very fast and cyclic data transmission and a high degree of certainty.
LON The communication standard in the field of building automation LON (Local Operating Network) is a communication system with multiple network connections for distributed applications, mainly in the field of commercial building automation.
Modbus Open Fieldbus Modbus is an open serial communication protocol based on a master/slave structure. The protocol is widely recognized because it can be implemented very easily on all types of serial interfaces.
MP-Bus [Organizer] MP-Bus
Profibus PROFIBUS DP/FMS Conforms to European standard EN50170 PROFIBUS is a high-speed bus that is widely used for distributed peripheral devices (PROFIBUS DP). In addition to PROFIBUS DP and FMS, Beckhoff also supports the PROFIBUS MC protocol for drive communication.
PROFINET Industrial Ethernet solutions from the PNO PROFINET is the open industrial Ethernet standard developed by the PNO (PROFIBUS User Organization), while internationally recognized IT standards such as TCP/IP are used for communication.
RS232/RS485 The most cost-effective solution for networking RS232 and RS485 are the 'traditional' serial interfaces and have always been widely used. Beckhoff's RS485/RS232 I/O modules use a simple, easy-to-implement serial communication protocol.
SERCOS III The bus from the field of drive engineering, SERCOS was originally developed as a high-speed fiber optic bus system for drives. Thanks to the development of the SERCOS Bus Coupler by Beckhoff, some of the advantages of the SERCOS bus (e.g. high data transfer rates and short cycle times) can now also be used for I/O peripherals.
USB The USB high-speed interface for laboratory use has become the standard interface for applications in the field of PC technology. Thanks to its high transmission rate, its flexible topology (via integrated hubs) and the USB Bus Coupler from Beckhoff, the USB system can be used as an alternative to fieldbuses in applications with short distances.