MC68HC908LJ12 Datasheet, PDF (58/413 Pages) Freescale Semiconductor, Inc – 8-bit microcontroller units

Technical Data — MC68HC908LJ12
Section 3. Random-Access Memory (RAM)
3.1 Contents
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
3.2 Introduction
This section describes the 512 bytes of RAM (random-access memory).
3.3 Functional Description
Addresses $0060 through $025F are RAM locations. The location of the
stack RAM is programmable. The 16-bit stack pointer allows the stack to
be anywhere in the 64k-byte memory space.
NOTE: For correct operation, the stack pointer must point only to RAM
locations.
Within page zero are 160 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.
MC68HC908LJ12 — Rev. 2.1
Freescale Semiconductor
Random-Access Memory (RAM)
Technical Data
59