C166: WORD VARIABLES ON ODD-BYTE BOUNDARIES

Information in this article applies to:

• C166 All Versions

QUESTION

I am porting a working application from an 8-bit microcontroller to a C16x device. The following code works just fine on the C16x:

#define test MVAR (unsigned short, 0x120000)
test = 100;

However, the following code does not work:

#define test MVAR (unsigned short, 0x120001)
test = 100;

When executing the second example, the program halts. What's going on?

ANSWER

The problem is that the C16x can only access words on word boundaries (even addresses). The C16x devices generate a Class B hardware trap when a word is accessed on an odd address (non-word boundary).

This problem doesn't occur on 8-bit devices because there is no boundary limitations on those parts.

Last Reviewed: Sunday, January 30, 2005