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MC9S12XE-Family Reference Manual , Rev. 1.07
Freescale Semiconductor
225
Chapter 4
Memory Protection Unit (S12XMPUV1)
Table 4-1. Revision History
4.1
Introduction
The MPU module provides basic functionality required to protect memory mapped resources from
undesired accesses. Multiple address range comparators compare memory accesses against eight memory
protection descriptors located in the MPU module to determine if each access is valid or not. The
comparison is sensitive to which bus master generates the access and the type of the access.
The MPU module can be used to isolate memory ranges accessible by different bus masters. It can be also
be used by an operating system or software kernel to isolate the regions of memory “l(fā)egally” available to
specific software tasks, with the kernel re-configuring the task specific memory protection descriptors in
supervisor state during task-switching.
4.1.1
Preface
The following terms and abbreviations are used in the document.
Table 4-2. Terminology
Version
Number
Revision
Date
Effective
Date
Author
Description of Changes
01.04
14 Sep
2005
14 Sep
2005
- added note to only use the CPU to clear the AE flag.
- added disclaimer to avoid changing descriptors while they are in
use because of other bus-masters doing accesses
- clarified that interrupt generation is independent of AEF bit state
- corrected preliminary statement about execution of violating
accesses
01.05
14 Mar
2006
14 Mar
2006
01.06
09 Oct
2006
09 Oct
2006
- made Revision History entries public
Term
MCU
MPU
CPU
XGATE
Meaning
Micro-Controller Unit
Memory Protection Unit
S12X Central Processing Unit (see S12XCPU Reference Manual)
XGATE Co-processor (see XGATE chapter)
supervisor state
user state
refers to the supervisor state of the S12XCPU (see S12XCPU Reference Manual)
refers to the user state of the S12XCPU (see S12XCPU Reference Manual)