What is the difference between microcontroller uart and modbus communication?
Modbus was invented by Modicon (now a brand of Schneider Electric) in 1979 and is the world's first bus protocol that is truly used in industrial sites.
The ModBus network is an industrial communication system that consists of programmable controllers and computers with intelligent terminals connected via public lines or local dedicated lines. Its system structure includes both hardware and software. It can be applied to various data acquisition and process monitoring.
The ModBus network has only one host and all communications are sent by him. The network can support as many as 247 remote slave controllers, but the actual number of slaves supported is determined by the communication equipment used. With this system, each PC can exchange information with the central host without affecting each PC performing its own control tasks.
(1) Standard, open, users can use the Modbus protocol free of charge, with no need to pay licensing fees, and will not infringe intellectual property rights. Currently, there are more than 400 manufacturers that support Modbus and more than 600 products that support Modbus.
(2) Modbus can support a variety of electrical interfaces, such as RS-232, RS-485, etc., and can also be transmitted on various media, such as twisted pair, optical fiber, and wireless.
(3) Modbus frame format is simple, compact and easy to understand. Users are easy to use, and vendor development is simple.
Modbus transmissionThere are two transmission modes to choose from in the ModBus system. The two transmission modes are equivalent to the ability of the slave PC to communicate. The choice depends on the ModBus host used. Only one mode can be used for each ModBus system, and two modes cannot be mixed. One mode is ASCII (American Information Interchange Code) and the other mode is RTU (Remote Terminal Device).
The user selects the desired mode, including serial communication parameters (baud rate, parity, etc.). When configuring each controller, all devices on a Modbus network must select the same transmission mode and serial port parameters. The selected ASCII or RTU method is only applicable to a standard Modbus network. It defines each bit of a message segment that is continuously transmitted on these networks and decides how to pack the message into a message field and how to decode it. On other networks (like MAP and Modbus Plus) Modbus messages are converted to frames that are not related to serial transmission.
Common MODBUS version1, MODBUS ASC II
2, MODBUS RTU
3, MODBUS/TCP
The UART is a universal serial data bus used for asynchronous communications. The bus bidirectional communication can achieve full duplex transmission and reception. In the embedded design, the UART is used for communication between the host and auxiliary devices, such as communication between a car stereo and an external AP, and communication with the PC includes communication with a monitoring debugger and other devices such as EEPROM.
UART communicationThe UART first converts the received parallel data into serial data for transmission. The message frame starts with a low start bit, followed by 7 or 8 data bits, one available parity bit and one or more high stop bits. When the receiver finds the start bit, it knows that the data is ready to be sent and tries to synchronize with the transmitter clock frequency. If a parity is selected, the UART adds a parity bit to the data bit. Parity bits can be used to help error checking.
During the TX process, the UART removes the start and end bits from the message frame, performs parity checking on the incoming bytes, and converts the data bytes from serial to parallel. The UART also generates additional signals to indicate the status of the transmission and reception. For example, if a parity error occurs, the UART sets the parity data direction and communication speed.
Data transmission can start with the least significant bit (LSB) first. However, some UARTs allow the flexibility to choose to send the least significant bit or the most significant bit (MSB) first.
The UART in the microcontroller transmits data at speeds ranging from a few hundred bits per second to 1.5 Mb. For example, high-speed UART communications embedded in the Elan SC520 microcontroller can be up to 1.1152 Mbps. The UART baud rate is also affected by the transmit and receive line pair distance (line length).
Currently, there are two types of hardware on the market that support asynchronous communications and support both asynchronous and synchronous communications. The former is the meaning of the UART name itself, which is called Serial Communication Interface (SCI) in Motorola microcontrollers; the Universal Synchronous Asynchronous Receiver Transmitter (USART) in Microchip microcontrollers and the UART in Fujitsu microcontrollers are Two typical examples.
The basic mode of data communication can be divided into parallel communication and serial communication:
1. Parallel communication: refers to the use of multiple data transmission lines to send a piece of data at the same time. It is characterized by fast transmission speeds and is suitable for short-distance communications, but requires high communication speeds for applications.
2. Serial communication: refers to using a transmission line to send data one bit at a time. It features simple communication lines, simple communication and cost reduction using simple cables, and is suitable for applications where long-distance communication is required, but transmission speed is slow.
Modbus is an application layer protocol. It is built on the basis of the underlying transmissions such as serial ports and network cables. Uart is just a serial protocol.
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