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Information in this article applies to:

  • MDK All Versions
  • Cx51 All Versions
  • C166 All Versions
  • C251 All Versions


My project includes a variable that I access using an absolute memory address. The µVision Debugger generates the following error whenever I try to write to the variable:

*** Error 65: Access violation at 0x00000004 : No 'write' permission

I have specified this memory area to the linker but I still receive this error.


When the µVision Debugger loads an executable program, it creates a memory map using the program and data segments from the program. Code segments are marked as executable while data segments are marked as read/write. All other memory is unmapped and is, therefore, not marked for any type of access.

The µVision Debugger checks that all memory accesses are made to objects that are defined in your C program. For any access that is outside of a defined C object, the µVision debugger generates an error 65: access violation message.

By default, the debugger allows only memory accesses to valid data objects. This is useful for finding uninitialized or incorrectly initialized pointers, for example. Usually, there is a programming error when you try to access unexpected locations.


Enable memory regions for absolute memory accesses using the MAP debugger command or the Debug - Memory Map dialog. Define all the memory ranges that your program is permitted to access. Ensure that you set the permissions (read, write, execute) for each range to match your actual hardware.

You may put the required MAP commands into a debugger INI file that can be entered under Project -> Options for Target -> Debug -> Initialization file. For example, the content of such a file may be:

MAP  0xF800, 0xF8FF  READ WRITE  // allow R/W access to IO space


  • Refer to MAP in the µVision3 User's Guide.



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

Last Reviewed: Wednesday, July 25, 2018

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