Home » Categories » Protocols » Modbus

What's the difference between Modbus ASCII and Modbus RTU?

The original Modbus specification included two possible transmission modes: ASCII and RTU. Modbus RTU mode is the most common implementation, using binary coding and CRC error-checking. Modbus ASCII messages (though somewhat more readable because they use ASCII characters) is less efficient and uses less effective LRC error checking. ASCII mode uses ASCII characters to begin and end messages whereas RTU uses time gaps (3.5 character times) of silence for framing. The two modes are incompatible so a device configured for ASCII mode cannot communicate with one using RTU.  Modbus ASCII messages require twice as many bytes to transmit the same content as a Modbus RTU message.

For additional information, please see the Modbus Protocol Specification document, "PI-MBUS-300.pdf."

Custom Fields
    Attachments (3) Attachments
    Comments Comments
    There are no comments for this article. Be the first to post a comment.
    Related Articles RSS Feed
    Do any Prosoft modules support Modbus UDP?
    Viewed 1 times since Mon, Aug 24, 2015
    How can a module's Modbus port, configured as a Slave port, detect communication loss with the Master port?
    Viewed 1 times since Tue, Nov 28, 2006
    If I am reading the value from ProSoft 4x register, and it represents a digital input or digital output, how is the value stored?
    Viewed 1 times since Tue, Nov 28, 2006
    I have multiple Modbus masters that need to communicate with 1 or more Modbus serial (RTU) slave devices. What product should be used??
    Viewed 1 times since Tue, Jan 23, 2007
    I am trying to use a ProSoft Modbus solution to send/receive data to a MSA Ultima X gas dectection system with Modbus interface and am having problems. How can I resolve this issue?
    Viewed 1 times since Thu, Apr 24, 2008
    How do I read/write Modbus binary data?
    Viewed 1 times since Wed, Nov 29, 2006
    What Modbus address would we need to put into the MODSIM32 simulator if we specified on the MVI56-MCM device address to 8680HEX (-31104 decimal) when the MVI56-mcm is the slave?
    Viewed 1 times since Tue, Nov 28, 2006
    How do I monitor the health of coms to my slaves when the module is a Master?
    Viewed 1 times since Wed, Nov 29, 2006
    How can I detect the feedback status of individual command successful or failed?
    Viewed 1 times since Wed, Nov 29, 2006
    Read Commands from my Modbus Master to a ProSoft MCM Slave are working but Write Commands are failing. How do I fix this?
    Viewed 1 times since Fri, Feb 8, 2008