HCS12 datasheet(423/452 Pages) FREESCALE

423 / 452 page

S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

423

point left of the MSB, so each line segment is effectively divided into 256

pieces. During execution of the TBL or ETBL instruction, the difference

between the end point y-value and the beginning point y-value (a signed

byte for TBL or a signed word for ETBL) is multiplied by the B accumulator

to get an intermediate delta-y term. The result is the y-value of the beginning

point, plus this signed intermediate delta-y value.

B.8.8 Extended Bit Manipulation

The M68HC11 CPU allows only direct or indexed addressing. This typically

causes the programmer to dedicate an index register to point at some

memory area such as the on-chip registers. The CPU12 allows all bit

manipulation instructions to work with direct, extended, or indexed

addressing modes.

B.8.9 Push and Pull D and CCR

The CPU12 includes instructions to push and pull the D accumulator and the

CCR. It is interesting to note that the order in which 8-bit accumulators A and

B are stacked for interrupts is the opposite of what would be expected for

the upper and lower bytes of the 16-bit D accumulator. The order used

originated in the M6800, an 8-bit microprocessor developed long before

anyone thought 16-bit single-chip devices would be made. The interrupt

stacking order for accumulators A and B is retained for code compatibility.

B.8.10 Compare SP

This instruction was added to the CPU12 instruction set to improve

orthogonality and high-level language support. One of the most important

requirements for C high-level language support is the ability to do arithmetic

on the stack pointer for such things as allocating local variable space on the

stack. The LEAS –5,SP instruction is an example of how the compiler could

easily allocate five bytes on the stack for local variables. LDX 5,SP+ loads

X with the value on the bottom of the stack and deallocates five bytes from

the stack in a single operation that takes only two bytes of object code.

HCS12 Datasheet(PDF) 423 Page - Freescale Semiconductor, Inc