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Information in this article applies to:

  • C166 All Versions
  • C251 All Versions
  • C51 All Versions
  • µVision Version 2 and Later


I want to use the current compiler version for new projects but I still need older compiler versions for making patches to existing projects.

Is it possible to install the newest and an older version of the compiler on the same PC?


Yes. µVision offers this flexiblity.

Before you upgrade or install a new release, copy the folder containing the older release (\KEIL\C51, \KEIL\C166, or \KEIL\C251) into a new folder and name the folder using the version number of the release. For example, copy Keil C51 Version 6.10 into the folder \KEIL\C51V610.

When you need to compile a project with this older version, you can set the Environment path to this folder. Set the following options under Project — Manage — Components, Environment and Books:

  • Use Settings from TOOLS.INI: OFF
  • BIN Folder: \Keil\C51V610\BIN

This modification also changes the INC and LIB folder to \KEIL\C51V610.

When you compile this project, it will be compiled using the compiler version in the \KEIL\C51V610 directory.

All other projects (where the environment has not been modified) will use the current tools in \KEIL\C51.

Note that this solution does not work for RealView MDK-ARM.  For MDK we recommend to make separate insallations in different root folders, for example C:\Keil305 (for MDK 3.05), C:\Keil310 (for MDK 3.10) an so on.




The following Discussion Forum threads may provide information related to this topic.

Last Reviewed: Friday, April 6, 2018

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