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Modbus/en: различия между версиями

Modbus/en (просмотреть исходный код)

Версия 16:34, 7 июля 2021

201 байт убрано ,  2 года назад
Часть переводимой страницы Протокол Modbus.
(Новая страница: «For the Modbus RTU Protocol, the 16-bit checksum (CRC) is calculated using the algorithm described in the [http://www.modbus.org/specs.php Modbus] specification…»)
(Часть переводимой страницы Протокол Modbus.)
 
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===Basics===
=== Fundamentals===


Basic concept
Modbus is a protocol of the applied (seventh) level of the [https://en.wikipedia.org/wiki/OSI_model OSI] model for data exchange, most often between automation devices and is implemented in the form of "request-reply protocol".  
Modbus is a Protocol of the applied (seventh) level of the [https://en.wikipedia.org/wiki/OSI_model OSI] model for data exchange, most often between automation devices and is implemented in the form of "request-reply protocol".  


In Wirenboard devices, Modbus data is transmitted over RS-485 serial communication lines. In serial lines RS-485 Protocol is half-duplex and works on the principle of "client-server". 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 Wirenboard devices, Modbus data is transmitted over RS-485 serial communication lines. In serial lines RS-485 Protocol is half-duplex and works on the principle of "client-server". 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.




There are two protocol specifications: Modbus RTU and Modbus ASCII. 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 no parity bit is transmitted, is transmitted to the Modbus RTU. This character allows you to transfer 1 byte of data. In Wiren Board devices, the parity bit is not transmitted and 2 stop bits are used. In Modbus ASCII, each byte is transmitted in two characters representing the ASCII codes of the lower and upper four-bit byte groups ([http://www.simplymodbus.ca/ASCII.htm пример]). The Modbus RTU allows you to transmit more information at the same serial line speed and it is used in the Wiren Board devices. All further description applies to Modbus RTU.
There are two protocol specifications: Modbus RTU and Modbus ASCII. 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. This character allows you to transfer 1 byte of data. In Wiren Board devices, the parity bit is not transmitted and 2 stop bits are used. In Modbus ASCII, each byte is transmitted in two characters representing the ASCII codes of the lower and upper four-bit byte groups ([http://www.simplymodbus.ca/ASCII.htm пример]). The Modbus RTU allows you to transmit more information at the same serial line speed and it is used in the Wiren Board devices. All further description applies to Modbus RTU.




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Holding Registers and Input Registers are represented by a two-byte word and can store values from 0 to 65535 (0x0000 — 0xFFFFF).
Holding Registers and Input Registers are represented by a two-byte word and can store values from 0 to 65535 (0x0000 — 0xFFFFF).
Input registers are read-only (e.g. current temperature). Storage registers support both read and write (to store settings). Currently, in many devices, particularly Wiren Board devices, these registers are not separated. Commands to read the storage register N and the input register N will access the same value in the address space of the device.
Input registers are read-only (e.g. current temperature). Storage registers support both read and write (to store settings). Currently, in many devices, particularly Wiren Board devices, these registers are not separated. Commands to read the storage register N and the input register N will access the same value in the address space of the device.


===Registers addresses and numbers===
===Registers addresses and numbers===
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[[File:SDM220_Template.png|700px|thumb|center|Template Fragment for SDM220 meter]]
[[File:SDM220_Template.png|700px|thumb|center|Template Fragment for SDM220 meter]]


=== Register reading and writing function codes ===
=== Register reading and writing function codes ===
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The following table shows the query and response data structures for the main Modbus functions.
The following table shows the query and response data structures for the main Modbus functions.


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{|class="wikitable" align="center"
{|class="wikitable" align="center"
!Function code || Request || Reply   
!Function code || Request || Reply   
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|-
|-
!    16 (Write Multiple register )
!    16 (Write Multiple register )
| <ul><li>The address of the first storage register for recording (16-bit</li><li>Number of holding registers to write (16 bits)</li><li>the Number of transmitted data bytes for the registers (8-bit)</li><li>Data (16 bytes per register)</li></ul> ||  <ul><li>The address of the first storage register (16 bits)</li><li>Number of written holding registers(16 bit)</li></ul>   
| <ul><li>The address of the first storage register for recording (16-bits)</li><li>Number of holding registers to write (16 bits)</li><li>the Number of transmitted data bytes for the registers (8-bit)</li><li>Data (16 bytes per register)</li></ul> ||  <ul><li>The address of the first storage register (16 bits)</li><li>Number of written holding registers(16 bit)</li></ul>   
|-
|-
|}
|}
</div>




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For the Modbus RTU Protocol, the 16-bit checksum (CRC) is calculated using the algorithm described in the [http://www.modbus.org/specs.php  Modbus] specification in ''the Modbus Serial Line Protocol and Implementation Guide, CRC-generation section''. The sending device generates two bytes of checksum based on the message data, and the receiving device recalculates the checksum and compares it with the received one. The coincidence of the accepted and calculated modbud RTU checksum is considered an indicator of successful data exchange.
For the Modbus RTU Protocol, the 16-bit checksum (CRC) is calculated using the algorithm described in the [http://www.modbus.org/specs.php  Modbus] specification in ''the Modbus Serial Line Protocol and Implementation Guide, CRC-generation section''. The sending device generates two bytes of checksum based on the message data, and the receiving device recalculates the checksum and compares it with the received one. The coincidence of the accepted and calculated modbud RTU checksum is considered an indicator of successful data exchange.


В случае ограниченных вычислительных ресурсов для вычисления контрольной суммы существует функция, использующая табличные значения (так же приведена в спецификации).
In the case of limited computing resources for the calculation of the checksum, there is a function that uses table values (also given in the specification).
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Источник — https://wirenboard.com/wiki/Служебная:Сравнение_версий/22217...52153