MC68HC08BD24 Datasheet, PDF (49/244 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Technical Data — MC68HC08BD24
Section 3. Random-Access Memory (RAM)
3.1 Contents
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
3.2 Introduction
This section describes the 512 bytes of RAM (random-access memory).
3.3 Functional Description
Addresses $0080 through $027F are RAM locations. The location of the
stack RAM is programmable. The 16-bit stack pointer allows the stack to
be anywhere in the 64-Kbyte memory space.
NOTE: For correct operation, the stack pointer must point only to RAM
locations.
Within page zero are 128 bytes of RAM. Because the location of the
stack RAM is programmable, all page zero RAM locations can be used
for I/O control and user data or code. When the stack pointer is moved
from its reset location at $00FF out of page zero, direct addressing mode
instructions can efficiently access all page zero RAM locations. Page
zero RAM, therefore, provides ideal locations for frequently accessed
global variables.
Before processing an interrupt, the CPU uses five bytes of the stack to
save the contents of the CPU registers.
NOTE: For M6805 compatibility, the H register is not stacked.
MC68HC08BD24 — Rev. 1.1
Freescale Semiconductor
Technical Data
49