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Download Products

Select a product from the list below to download the latest version.

Version 5.21a (August 2016)
Development environment for Cortex and ARM devices.
C51 Download C51
Version 9.56 (August 2016)
Development tools for all 8051 devices.
C251 Download C251
Version 5.58 (October 2015)
Development tools for all 80251 devices.
C166 Download C166
Version 7.55 (April 2015)
Development tools for C166, XC166, & XC2000 MCUs.

Keil products use a License Management system - without a current license the product runs as a Lite/Evaluation edition with a few Limitations.

Maintenance Status and Previous Versions

Enter a valid Product Serial Number (PSN) or License Code (LIC) to get access to all product versions available to you, or to check the status of your support and maintenance agreement.


Further information about installing your software is available in the Read Me First brochure.

Notes Note

  • Use a current Product Serial Number (PSN) to get a License Code (LIC) that converts the Lite/Evaluation version to a full edition
  • Evaluation editions of Keil software products do not require a Product Serial Number or License Code.
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Acquisition of ARM Holdings plc. by SoftBank Group Corp.

We are pleased to inform you that on 5 September 2016, SoftBank Group Corp. acquired ARM Holdings Plc. ARM will continue to operate as an independent business within the SoftBank group.

Any current agreements between ARM Ltd (or other ARM group companies, as applicable) you / your company remain in effect as between the parties, and the parties will continue to be bound by and perform the obligations in such agreements. If you have any queries please direct these to