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C51: HOW TO USE 256 BYTES DATA SPACE


Information in this article applies to:

  • C51 All Versions

QUESTION

I have an 8051 device that has 256 bytes DATA RAM, but it appears that I can only access the first 128 bytes. How can I enable the remaining memory?

ANSWER

The 8051 architecture differs between DATA and IDATA. When a device has 256 bytes on-chip RAM space, the first 128 bytes can be only accessed in DATA space whereas the entire 256 bytes space can be accessed as IDATA.

In the C compiler you must define variables that should be placed above the 128 bytes limit using the idata memory type.

Example:

unsigned char idata uc;  // variable in IDATA can be located above 0x80

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Last Reviewed: Wednesday, November 15, 2006


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