C51: FAR DATA POINTER BOUNDARIES

Information in this article applies to:

• C51 All Versions

SYMPTOM

When I try to access a large data buffer using a far pointer, the pointer won't increment over a 64k boundary.

CAUSE

The far data pointer type is only 16 bits long, so it can only "see" 64k of space.

RESOLUTION

There is no pointer type, in C51, that can see more than 64k of data space at a time. However, there are ways around this. For example:

#include <absacc.h>

unsigned char far *farBuff = FARRAY(unsigned char, 0x110000);
unsigned long i;

for (i=0; i<0x18000; i++)
{
  userFunc(farBuff[i]);
}

SEE ALSO

• Refer to Far Memory in the C51/CX51 User's Guide.
• Refer to Generic and Far Pointers in the C51/CX51 User's Guide.

MORE INFORMATION

• CX51: ARRAY INDEX ARITHMETIC

FORUM THREADS

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

• Compiling Error with FAR declaration
• pointer cannot cross 64k boundary

Last Reviewed: Friday, July 15, 2005