C51: XWORD Macro Questions

Information in this article applies to:

• C51 All Versions

QUESTION

When using the XBYTE MACRO, my data is stored exactly where it is supposed to be. All works OK. When I use the XWORD MACRO, the data does not go to the specified address.

What's happening here?

ANSWER

The XBYTE macro is defined to access memory as a large array of unsigned char. For example:

xdata unsigned char XBYTE [0x10000] _at_ 0;

The XWORD macro is defined to access memory as a large array of unsigned int. For example:

xdata unsigned int XWORD [0x8000] _at_ 0;

XBYTE[100] accesses the BYTE at address 100. While XWORD[100] accesses the WORD at address 200.

In a nutshell, the XWORD macro only accesses 16-bit values on even boundaries. The index is NOT the address, but the index of the word. The address is 2 times the index. This is the same as indexing into an array of ints that start at address 0.

MORE INFORMATION

• Refer to XBYTE in the Cx51 User's Guide.
• Refer to XWORD in the Cx51 User's Guide.

SEE ALSO

• C51: Reserving Memory Accessed With XBYTE and XWORD

Last Reviewed: Thursday, February 25, 2021