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C251: Using Version 3 Compiler with Version 4 LIC

Information in this article applies to:

  • C251 Version 4


I purchased a C251 compiler license and received C51 Version 4 and a Product Serial Number (PSN). The project I'm working on requires the C251 Version 3 compiler. How can I install C251 Version 3 instead of C251 Version 4?


To downgrade C251 Version 4 to C251 Version 3...

  • Install Version 4 from the CD-ROM and add your license as explained in the Licensing User's Guide.
  • Download the file attached to this article using your License ID Code (LIC).
  • Copy the downloaded file C251.DLL to the folder Keil\C251\BIN.
  • Open TOOLS.INI (located in your installation folder) with a text editor.
    • Look in the section [C251] for the line LIC0=XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX.
    • Copy that line and change LIC0 to SN in the copied line so that it reads: SN=XXXXX-XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
    • Save and close TOOLS.INI
  • Copy the Verison 3 *.EXE files C251.EXE and L251.EXE to the folder Keil\C251\BIN.

You are now able to run C251 Version 3 components.


Request the files attached to this knowledgebase article.

Last Reviewed: Tuesday, January 12, 2021

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