
Chapter 17 Memory Protection Unit (S12XMPUV2)
MC9S12XF - Family Reference Manual, Rev.1.19
Freescale Semiconductor
811
17.3.1.11 MPU Descriptor Register 5 (MPUDESC5)
Figure 17-13. MPU Descriptor Register 5 (MPUDESC5)
Read: Anytime
Write: Anytime
Table 17-13. MPUDESC5 Field Descriptions
17.4
Functional Description
The MPU module provides memory protection for accesses coming from multiple masters in the system.
This is done by monitoring bus trafc of each master and compare this with the conguration information
from a set of N1 programmable descriptors located in the MPU module. If the MPU detects an access
violation caused by the S12X CPU, it will assert the CPU access violation interrupt signal. If the MPU
detects an access violation caused by a bus master other than the S12X CPU, it raises an access error signal.
Please refer to the documentation chapter of the individual master modules (i.e. XGATE, etc.) for more
information about the access error condition.
Violating accesses are not executed. The return value of a violating read access is undened for both 8 bit
and 16 bit accesses.
NOTE
Accesses from BDM are not restricted. BDM hardware accesses always
bypass the MPU. During execution of BDM rmware code S12X CPU
accesses are masked from the MPU as well.
17.4.1
Protection Descriptors
Each of the N protection descriptors can be used to restrict the allowed types of memory accesses for a
given memory range. Each of these memory ranges can cover up the entire dened MPU address range.
This can be the full 23 bits global memory range (8 MBytes) of the SoC.
Address: Module Base + 0x000B
76543210
R
HIGH_ADDR[10:3]
W
Reset
1(1)
1. These bits are intialized to the upper boundary of the MPU address range by a system reset. Depending on dened descriptor
granularity and MPU address range some of these bits may not be writeable.
Field
Description
7–0
HIGH_ADDR[
10:3]
Memory range upper boundary address bits — The HIGH_ADDR[10:3] bits represent bits [10:3] of the
global memory address that is used as the upper boundary for the described memory range. These bits are
intialized to the upper boundary of the MPU address range by a system reset.
1. The number of implemented descriptors is a conguration option dened at SoC level. Please refer to the MCU toplevel chapter
for details.