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Chapter 17 Memory Protection Unit (S12XMPUV2)
MC9S12XF - Family Reference Manual, Rev.1.19
808
Freescale Semiconductor
17.3.1.6
MPU Descriptor Register 0 (MPUDESC0)
Figure 17-8. MPU Descriptor Register 0 (MPUDESC0)
Read: Anytime
Write: Anytime
Table 17-8. MPUDESC0 Field Descriptions
A descriptor can be congured as valid for more than one bus-master at the same time by setting multiple
Master select bits to one. Setting all Master select bits of a descriptor to zero disables the descriptor. Bits
for non-implemented masters cannot be written to and always read zero.
Address: Module Base + 0x0006
76543210
R
MSTR0
MSTR1
MSTR2
MSTR3
LOW_ADDR[22:19]
W
Reset
1(1)
1. initialized as set for descriptor 0 only, cleared for all others
11
1(2)
2. initialized as set for descriptor 0 only, if respective master is implemented on the device
0(3)
3. These bits are intialized to the lower 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
MSTR0
Master 0 select bit — If this bit is set the descriptor is valid for bus master 0 (CPU in supervisor state).
6
MSTR1
Master 1 select bit — If this bit is set the descriptor is valid for bus master 1 (CPU in user state). This bit can
only be set if the CPU supports user state.
5
MSTR2
Master 2 select bit — If this bit is set the descriptor is valid for bus master 2 (XGATE). This bit can only be set
if there is an XGATE implemented on the SoC.
4
MSTR3
Master 3 select bit — If this bit is set the descriptor is valid for bus master 3 (FlexRay).(1)
1. Please refer Refernce Guide for information about the availability and function of Master 3 (see
1.9 MPU Conguration).3–0
LOW_ADDR
[22:19]
Memory range lower boundary address bits — The LOW_ADDR[22:19] bits represent bits [22:19] of the
global memory address that is used as the lower boundary for the described memory range. These bits are
intialized to the lower boundary of the MPU address range by a system reset.