MC68HC08AS20 Datasheet, PDF (51/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Advance Information — MC68HC08AS20
Section 3. Random-Access Memory (RAM)
3.1 Contents
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
3.2 Introduction
This section describes the 640 bytes of random-access memory (RAM).
3.3 Functional Description
Addresses $0050–$02CF are RAM locations. The location of the stack
RAM is programmable. The 16-bit stack pointer allows the stack to be
anywhere in the 640-byte memory space.
NOTE: For correct operation, the stack pointer must point only to RAM
locations.
Within page zero are 176 bytes of RAM. Because the location of the
stack RAM is programmable, all page zero RAM locations can be used
for input/output (I/O) control and user data or code. When the stack
pointer is moved from its reset location at $00FF, direct addressing
mode instructions can access all page zero RAM locations efficiently.
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 M68HC05, M6805, and M146805 compatibility, the H register is not
stacked.
MC68HC08AS20 — Rev. 4.1
Freescale Semiconductor
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