Section 17. Random-Access Memory (Ram) - Motorola MC68HC908GP32 Technical Data Manual

Technical Data – MC68HC908GP32•MC68HC08GP32
17.1 Contents
17.2 Introduction
17.3 Functional Description
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NOTE:
MC68HC908GP32 MC68HC08GP32
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MOTOROLA
Freescale Semiconductor, Inc.

Section 17. Random-Access Memory (RAM)

17.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
17.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
This section describes the 512 bytes of RAM (random-access memory).
Addresses $0040 through $023F 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.
For correct operation, the stack pointer must point only to RAM
locations.
Within page zero are 192 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.
For M6805 compatibility, the H register is not stacked.
Rev. 6
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Random-Access Memory (RAM)
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Technical Data
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