MC68HC908LD64 Datasheet, PDF (61/362 Pages) Freescale Semiconductor, Inc – Microcontrollers

Data Sheet — MC68HC908LD64
Section 3. Random-Access Memory (RAM)
3.1 Contents
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
3.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
3.2 Introduction
This section describes the 2,048 bytes of RAM (random-access
memory).
3.3 Functional Description
The RAM is divided into two blocks. Addresses $0080 through $047F
are locations for general use. Addresses $0800 through $0BFF are
locations for the OSD display RAM (see 18.6 OSD Screen Memory
Map). 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.
MC68HC908LD64 — Rev. 3.0
Freescale Semiconductor
Random-Access Memory (RAM)
Data Sheet
61