Modbus RTU vs. ASCII
A free video tutorial from Emile Ackbarali
Software Developer, Systems Integrator and Entrepreneur
27 courses
33,600 students
Lecture description
When the Modbus protocol was developed, the specification implemented two different modes of operation: Modbus RTU and Modbus ASCII. In this lecture we will cover:
Modbus RTU vs. Modbus ASCII
Advantages of RTU over ASCII
Very high prevalence of Modbus RTU over ASCII
Learn more from the full course
Mastering Modbus RS485 Network Communication
Learn how to design, implement and manage the most popular automation networking system in the world.
03:31:35 of on-demand video • Updated May 2026
The Origins of the Modbus Protocol and RS485
Understand Memory Address vs. Memory Value
Memory Addressing Conventions
Typical Device Memory Map
Protocol Network Messaging
RS485 Standard and Device Interconnection
Protocol Data Frame Structure
Query - Response Cycle
Function Codes and Master Commands
Modbus Simulation using FREE Simulation Software
Troubleshooting and Exception Codes
Floating Point Data Structure
Modbus Communication with Programmable Logic Controller
Full Course Support Documentation
English
When the Modbus protocol was developed the specification implemented two different modes of operation the two modes were Modbus RTU and Modbus ASCII. ASCII is pronounced "as-key" and is really the American standard code for information interchange. As time went along however Modbus RTU began to be used more and more over Modbus ASCII. The main reason was that Modbus RTU was much more efficient in transporting data. It could transport the same amount of data in roughly half the time as Modbus ASCII hence it grew in popularity. Nowadays Modbus ASCII has all but disappeared. Almost every new and current device that supports Modbus supports the Modbus RTU mode hence in this course we will not be speaking about Modbus ASCII at all. We will be concentrating exclusively on Modbus RTU. So whenever I refer to the Modbus protocol in this course I will in fact be referring to the Modbus protocol implemented as Modbus RTU mode. OK.