MC68HC08LT8 Datasheet, PDF (29/156 Pages) Freescale Semiconductor, Inc – Microcontrollers

Random-Access Memory (RAM)
2.4 Random-Access Memory (RAM)
The 512 bytes RAM are located from $0080 through $027F. 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 128 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, 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 CPU
registers.
NOTE
For M6805 compatibility, 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 may overwrite data in
the RAM during a subroutine or during the interrupt stacking operation.
2.5 Read-Only Memory (ROM)
The 8,192 bytes user ROM are located from $DE00 through $FDFF, plus a block of 48 bytes for user
interrupt vectors from $FFD0 through $FFFF.
MC68HC08LT8 Data Sheet, Rev. 1
Freescale Semiconductor
29