- #IS MODBUS A FORM OF SERIAL COMMUNICATION PROTOCOL SERIAL#
- #IS MODBUS A FORM OF SERIAL COMMUNICATION PROTOCOL CODE#
For reference - in Modbus TCP, the maximum packet length is 260 bytes.
#IS MODBUS A FORM OF SERIAL COMMUNICATION PROTOCOL SERIAL#
The maximum ADU size in serial communication lines is 253 bytes (1 byte of the address and two bytes of the checksum are subtracted from the maximum 256 bytes allowed by the specification). For serial lines, the device address is passed in the ADU header, and the CRC16 checksum is passed at the end. Includes a physical layer-specific part of the package and PDU. ADU (Application Data Unit) is a complete Modbus package.
#IS MODBUS A FORM OF SERIAL COMMUNICATION PROTOCOL CODE#
A PDU (Protocol Data Unit) is a common part of a MODBUS package that includes the function code and data of the package. The Modbus data package looks as shown in the figure. The master has no address, the transmission of messages from the device server to the host without asking the host in the protocol is not provided. The master device periodically polls the slave or server. All further description applies to Modbus RTU. The Modbus RTU allows you to transmit more information at the same serial line speed and it is used in the Wiren Board devices. In Modbus ASCII, each byte is transmitted in two characters representing the ASCII codes of the lower and upper four-bit byte groups ( пример). In Wiren Board devices, the parity bit is not transmitted and 2 stop bits are used. This character allows you to transfer 1 byte of data.
![is modbus a form of serial communication protocol is modbus a form of serial communication protocol](https://i0.wp.com/microdigisoft.com/wp-content/uploads/2021/11/ESP32-Modbus-RS485.png)
An 11-bit character consisting of 1 start bit, 8 data bits (starting with the lower bit), a parity bit (optional), and 2 stop bits if no parity bit is transmitted, or 1 stop bit if parity bit is transmitted, is transmitted to the Modbus RTU.
![is modbus a form of serial communication protocol is modbus a form of serial communication protocol](https://realpars.com/wp-content/uploads/2018/12/Modbus-Communication-over-Serial-RS-485-Physical-Media.jpg)
There are two protocol specifications: Modbus RTU and Modbus ASCII. Each device on the network (except the master, see below) has an address from 1 to 247, address 0 is used for broadcasting to all devices, and addresses 248-255 are considered reserved according to the Modbus specification, their use is not recommended. In serial lines RS-485 Protocol is half-duplex and works on the principle of "client-server".
![is modbus a form of serial communication protocol is modbus a form of serial communication protocol](https://planet.com.tw/storage/products/49323/box_IMG-2400T1.jpg)
In Wirenboard devices, Modbus data is transmitted over RS-485 serial communication lines. Modbus is a protocol of the applied (seventh) level of the OSI model for data exchange, most often between automation devices and is implemented in the form of "request-reply protocol".