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C51: Evaluation Compiler for Cypress Devices

Information in this article applies to:

  • C51 evaluation Versions 6.0 and greater


The Cypress PSoC Creator™ (or the EZ-USB development system) include the Keil C51 compiler tools. The evaluation C51 compiler is limited to 2048 decimal bytes (800H). Cypress support states that Keil has a 4,096 byte version (1000H) for EZ-USB parts and other Cypress 8051 parts. Where is the 4K version of the C51 evaluation compiler?


Cypress delivers the 4K version of the Keil C51 compiler on some versions of their development kits. This 4K version was developed strictly for 8051-based devices from Cypress. This compiler will not work for ARM-based microcontrollers from Cypress. The Keil tools are part of the Cypress tool installation, i.e., they would be included in a subfolder similar to this:

Program Files (x86)\Cypress\PSoC Creator\x.x\PSoC Creator\import\keil\pk51

... where the "x" is the current version of the tools.

The Keil web site only maintains the standard 2K edition of the C51 evaluation tools.


Important Note as of January 2018

In case of problems the current workarounds for the 9939 error code is:

Unlock the 4K version

To unlock the 4K version of the tools:

For Users that Purchased a Full Keil License

Rather than use the 4K version of the license in the Cypress tools, have the Cypress tools point to the full Keil license.

  • If not already done, follow these steps to get and install a LIC. If there is not a separate copy of the Keil tools on the PC, open the UV4.exe located in the ...PSoC Creator\import\keil\pk51\Uv4\ folder, to request a LIC.
  • Open Windows Explorer and find the \Keil\PK51\ subfolder within the Cypress tools installation on your PC. Find the tools.ini file within that subfolder.
  • Follow step 2 of this page to modify the Keil tools.ini file with the Keil LIC.




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

Last Reviewed: Tuesday, March 5, 2019

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