MC9S08DZ128 Datasheet, PDF (61/458 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 4 Memory
debug interface) and verifying that FLASH is blank. To avoid returning to secure mode after the next reset,
program the security bits (SEC) to the unsecured state (1:0).
4.4 Memory Management Unit
The memory management unit (MMU) allows the program and data space for the HCS08 Family of
Microcontrollers to be extended beyond the 64K CPU addressable memory map. The extended memory
when used for data can also be accessed linearly using a linear address pointer and data access registers.
4.4.1 Features
Key features of the MMU module are:
• Memory Management Unit extends the HCS08 memory space
— up to 128K for program and data space
• Extended program space using paging scheme
— PPAGE register used for page selection
— fixed 16K byte memory window
— architecture supports eight 16K pages
• Extended data space using linear address pointer
— 17-bit linear address pointer
— linear address pointer and data register provided in direct page allows access of complete
FLASH memory map using direct page instructions
— optional auto increment of pointer when data accessed
— supports a 2s complement addition/subtraction to address pointer without using any math
instructions or memory resources
— supports word accesses to any address specified by the linear address pointer when using
LDHX, STHX instructions
4.4.2 Memory Expansion
The HCS08 Core architecture limits the CPU addressable space available to 64K bytes. The Program Page
(PPAGE) allows for integrating up to 128K of FLASH into the system by selecting one of the 16K byte
blocks to be accessed through the Paging Window located at 0x8000-0xBFFF. The MMU module also
provides a linear address pointer that allows extension of data access up to 128K.
4.4.2.1 Program Space
The PPAGE register holds the page select value for the Paging Window. The value in PPAGE can be
manipulated by using normal read and write instructions as well as the CALL and RTC instructions. The
user should not change PPAGE directly when running from paged memory, only CALL and RTC should
be used.
MC9S08DZ128 Series Data Sheet, Rev. 1
Freescale Semiconductor
61