Intel Microcontroller, 80C196NU Assembly Language Addressing Mode Selections, Extended Addressing

PROGRAMMING CONSIDERATIONS

4.3ASSEMBLY LANGUAGE ADDRESSING MODE SELECTIONS

The assembly language simplifies the choice of addressing modes. Use these features wherever possible.

4.3.1Direct Addressing

The assembly language chooses between direct and zero-indexed addressing depending on the memory location of the operand. Simply refer to the operand by its symbolic name. If the operand is in the lower register file, the assembly language chooses a direct reference. If the operand is elsewhere in memory, it chooses a zero-indexed reference.

4.3.2Indexed Addressing

The assembly language chooses between short-indexed and long-indexed addressing depending on the value of the index expression. If the value can be expressed in eight bits, the assembly lan- guage chooses a short-indexed reference. If the value is greater than eight bits, it chooses a long- indexed reference.

4.3.3Extended Addressing

If the operand is outside page 00H, then you must use the extended load and store instructions, ELD, ELDB, EST, and ESTB.

4.4DESIGN CONSIDERATIONS FOR 1-MBYTE DEVICES

In general, you should avoid creating tables or arrays that cross page boundaries. For example, if you are building a large array, start it at a base address that will accommodate the entire array within the same page. If you cannot avoid crossing a page boundary, keep in mind that you must use extended instructions to access data outside the original page.

4.5SOFTWARE STANDARDS AND CONVENTIONS

For a software project of any size, it is a good idea to develop the program in modules and to es- tablish standards that control communication between the modules. These standards vary with the needs of the final application. However, all standards must include some mechanism for passing parameters to procedures and returning results from procedures. We recommend that you use the conventions adopted by the C programming language for procedure linkage. These standards are usable for both the assembly language and C programming environments, and they offer compat- ibility between these environments.

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