Tuesday, January 10, 2012

Difference between Modbus ASCII and Modbus RTU

The original specification of Modbus contained two probable modes of transmission, they are: RTU and ASCII. The mode of Modbus RTU is the majority common accomplishment, using CRC error-checking and binary coding. The message of Modbus ASCII is less competent and uses less efficient error checking of LRC. The mode of ASCII uses characters of ASCII to start and end messages where RTU uses silence time gaps for framing. The 2 modes are incompatible so a device designed for ASCII mode can not correspond with the device is using RTU. Messages of Modbus ASCII need twice as many bytes to send out the same substance as a message of Modbus RTU.

The difference Modbus RTU to Modbus ASCII is clear termination. Different methods of encryption by Modbus ASCII are format of ASCII code. The Modbus RTU, binary memory size is less data to be transmitted at the same time to many Modbus RTU, So definitely that will be sent the messages faster when great data amounts. The same theory is utilized for sending data is similar.

Both Modbus ASCII and Modbus RTU address can recognize. The different of Modbus ASCII is a direct Hexadecimal base with2 bytes while Modbus RTU is using one byte. The serial links of Modbus use 2 essential types of transmission, ASCII or RTU and remote terminal units (RTUs). The transmission mode of the serial communication identifies how the messages are encrypted. All messages in an ASCII format is readable. The protocol of Modbus RTU that uses format of binary it makes the message is unreadable.

All the nodes on a network segment of Modbus have to use the same serial transmission form. A device that designed for the Modbus ASCII is not capable to transmit the messages using Modbus RTU.


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