HCS12 datasheet(426/452 Pages) FREESCALE

426 / 452 page

S12CPUV2 Reference Manual, Rev. 4.0

426

Freescale Semiconductor

The CPU12 has special sign extension instructions to allow easy

type-casting from smaller data types to larger ones, such as from char to

integer. This sign extension is automatically performed when an 8-bit value

is transferred to a 16-bit register.

C.3 Parameters and Variables

High-level languages make extensive use of the stack, both to pass

variables and for temporary and local storage. It follows that there should be

easy ways to push and pull each CPU register, stack pointer based indexing

should be allowed, and that direct arithmetic manipulation of the stack

pointer value should be allowed. The CPU12 instruction set provided for all

of these needs with improved indexed addressing, the addition of an LEAS

instruction, and the addition of push and pull instructions for the D

accumulator and the CCR.

C.3.1 Register Pushes and Pulls

The M68HC11 has push and pull instructions for A, B, X, and Y, but requires

separate 8-bit pushes and pulls of accumulators A and B to stack or unstack

the 16-bit D accumulator (the concatenated combination of A:B). The PSHD

and PULD instructions allow directly stacking the D accumulator in the

expected 16-bit order.

Adding PSHC and PULC improved orthogonality by completing the set of

stacking instructions so that any of the CPU registers can be pushed or

pulled. These instructions are also useful for preserving the CCR value

during a function call subroutine.

HCS12 Datasheet(PDF) 426 Page - Freescale Semiconductor, Inc