HCS12 datasheet(425/452 Pages) FREESCALE

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S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

425

C.1 Introduction

Many programmers are turning to high-level languages such as C as an

alternative to coding in native assembly languages. High-level language

(HLL) programming can improve productivity and produce code that is more

easily maintained than assembly language programs. The most serious

drawback to the use of HLL in MCUs has been the relatively large size of

programs written in HLL. Larger program ROM size requirements translate

into increased system costs.

This appendix identifies CPU12 instructions and addressing modes that

provide improved support for high-level language. C language examples are

provided to demonstrate how these features support efficient HLL structures

and concepts. Since the CPU12 instruction set is a superset of the

M68HC11 instruction set, some of the discussions use the M68HC11 as a

basis for comparison.

C.2 Data Types

The CPU12 supports the bit-sized data type with bit manipulation

instructions which are available in extended, direct, and indexed variations.

The char data type is a simple 8-bit value that is commonly used to specify

variables in a small microcontroller system because it requires less memory

space than a 16-bit integer (provided the variable has a range small enough

to fit into eight bits). The 16-bit CPU12 can easily handle 16-bit integer types

and the available set of conditional branches (including long branches)

allow branching based on signed or unsigned arithmetic results. Some of

the higher math functions allow for division and multiplication involving

32-bit values, although it is somewhat less common to use such long values

in a microcontroller system.

Reference Manual — S12CPUV2

Appendix C. High-Level Language Support

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