MC68HC908KX8 Datasheet, PDF (47/310 Pages) Motorola, Inc – Microcontrollers

Technical Data — MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8
Section 3. Random-Access Memory (RAM)
3.1 Contents
3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3 Functional Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.2 Introduction
This section describes the 192 bytes of random-access memory (RAM).
3.3 Functional Description
Addresses $0040–$00FF 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.
Before processing an interrupt, the CPU uses five bytes of the stack to
save the contents of the CPU registers.
NOTE: For M6805, M146805 and M68HC05compatibility, the H register is not
stacked.
During a subroutine call, the CPU uses two bytes of the stack to store
the return address. The stack pointer decrements during pushes and
increments during pulls.
NOTE:
Be careful when using nested subroutines. The CPU could overwrite
data in the RAM during a subroutine or during the interrupt stacking
operation.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
MOTOROLA
Random-Access Memory (RAM)
Technical Data
47