Cs Modbus

An industrial communications protocol used for connecting industrial electronic devices.



About Modbus

With Cs/Modbus, you can use either ASCII frames or RTU frames, or both at the same time if you have multiple serial interfaces. Cs/Modbus module supports any number of communications channels.

Modbus-S is a Modbus Slave (server) software component enabling an embedded system to communicate to a Modbus Master (client).

Modbus-M is a Modbus Master (client) component that enables communication to a Modbus Slave.

Cs/Modbus module enables a developer to read or write integer, floating-point (assuming Daniels extensions), and discrete values from and to the target system.

modbus schematic

Key Features

The features of Cs/Modbus module include:

  • Allows for multiple RS-232C and/or RS-485 ports on the same target (limited only by the number of serial ports available)
  • The baud rate for each port is independently adjustable
  • Select either Modbus ASCII or RTU on a per-channel basis
  • Easily assign nearly any application variable to any Modbus holding register (up to 65536), input register (up to 65536), coil (up to 65536), or input status (up to 65536)
  • Complete, clean ANSI C source code included
  • Scalable from 6K to 15K bytes. Compile only the function codes necessary for the target
  • Works with any CPU (8-, 16-, 32-, 64-bit, or DSP)
  • Works with or without an RTOS kernel
  • Easily configurable



Key Specifications

Unlimited number of ‘channels’ (limited only by the number of serial interfaces)

ASCII or RTU mode selectable on a per-channel basis

Floating-point support through “Daniel’s Extensions”

Modbus Slave or Master possible on the same product

Adjustable baud rate on a per channel-basis

Easily assign application variables to Modbus registers, coils, and discrete inputs

Works with any processor (8-, 16-, 32-, 64-bit, or DSP)

Works with or without an RTOS kernel

Easily configurable

ANSI C source code provided

Scalable from 6K to 15K bytes of code space


Function Codes

Supported Modbus function codes:

Function Code

1 Coil Read
2 Discrete Input Read
3 Holding Register Read
4 Input Register Read
5 Write Single Coil
6 Write Single Holding Register
8 Diagnostic Loopback
15 Write Multiple Coils
16 Write Multiple Holding Registers
20 File Read
21 File Write


Commercial License

Click here for more details


Technical Support

Technical Support Plan

Technical support services for any of the Cs/ software is readily available to all customers currently using or interested in the Cs/ family of RTOS components.

If you are currently without technical support for the Cs/OS software don’t go at it alone. Please contact us to learn how our Cs/OS product experts, with years of embedded software experience, can save you valuable engineering time and money.

Click here for more details


Consulting Services

Specialized Engineering Services

Do you need specialized assistance with your Cesium-based embedded project? Do you need real-time embedded software expertise for your mission critical application? For these or any other embedded software projects, help is available via our Consulting Services that are tailored to your unique needs. Please contact us with your requirements to learn how we can quickly deliver our expertise to your team.

Click here for more details



Cesium software includes comprehensive documentation, full source code, powerful debugging features, and support for a huge range of CPU architectures.


Cesium software offers unprecedented ease-of-use, a small memory footprint, remarkable energy efficiency, and all with a full suite of protocol stacks.


Engineers across the world building industrial controls, medical devices, and aerospace systems know they can rely on Cesium software for the foundation of exceptional products.