MC68HC908MR8 Datasheet, PDF (53/372 Pages) Motorola, Inc – Microcontrollers

Technical Data — MC68HC908MR8
Section 3. Random-Access Memory (RAM)
3.1 Contents
3.2 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
3.3 Functional Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
3.2 Introduction
This section describes the 256 bytes of random-access memory (RAM)
on the MC68HC908MR8.
3.3 Functional Description
Addresses $0060–$015F 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 160 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 efficiently 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 central processor unit (CPU) registers.
NOTE: For M6805 compatibility, the H register is not stacked.
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor
Random-Access Memory (RAM)
Technical Data
53