HC805K3GRSSLASHD datasheet(37/119 Pages) NXP

37 / 119 page

General Release Specification

Registers

MC68HC805K3 — Rev. 1.0

Central Processing Unit Core

3.3.1 Stack Pointer (SP)

The stack pointer shown in Figure 3-1 is a 16-bit register internally. In

devices with memory maps less than 64 Kbytes, the unimplemented

upper address lines are ignored. The stack pointer contains the address

of the next free location on the stack. When accessing memory, the 11

most significant bits are permanently set to 00000000111. The five least

significant register bits are appended to these 11 fixed bits to produce an

address within the range of $00FF to $00E0. Subroutines and interrupts

may use up to 32 ($20) locations. If 32 locations are exceeded, the stack

pointer wraps around to $00FF and writes over the previously stored

information.

3.3.2 Program Counter (PC)

The program counter shown in Figure 3-1 is a 16-bit register internally.

The program counter contains the address of the next instruction or

operand to be fetched. The six most significant bits of the program

counter are ignored internally and appear as 000000 when stacked onto

the RAM.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

HC805K3GRS/D Datasheet(PDF) 37 Page - NXP Semiconductors