Newbie question: Modbus TCP/Serial/ASCII/RTU


Thread Starter


As far as I understand, the Modbus is either defined for serial (RS232/RS485) or TCP/IP protocol layer. What does RTU and ASCII mode mean in that context? Do I have the possibility to operate Modbus in all of the following combinations:
- Serial and RTU
- Serial and ASCII
- TCP/IP and RTU
RTU mode is binary, while ASCII mode is human readable verbose ASCII. They are both Serial. You should refer to the data at for how to use Modbus. As far as _I_ know, you can use either RTU or ASCII over TCP.

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The choice between RTU and ASCII modes only exists in for Modbus serial connections. RTU mode is generally limited to direct connections where characters will not be delayed and cause a false end-of-message, while ASCII mode is used for modem and radio links where character delays become an issue. Modbus/TCP embeds an RTU message within the TCP packet and ignores character timing, so there is no requirement or option for ASCII mode.