Fujitsu FR81S User Manual
CHAPTER 3: CPU
10. Memory Protection Function (MPU)
FUJITSU SEMICONDUCTOR LIMITED
CHAPTER : CPU
FUJITSU SEMICONDUCTOR CONFIDENTIAL
42
[bit12] UIE (User Mode Instruction Fetch Enable)
This bit is for enabling instruction fetch in user mode for the specified protection area.
UIE
Access to the specified protection area
0
Instruction fetch not permitted in user mode (initial value)
1
Instruction fetch permitted in user mode
[bit11] URE (User Mode Read Access Enable)
This bit is for enabling data read access in user mode for the specified protection area.
URE
Access to the specified protection area
0
Read access not permitted in user mode (initial value)
1
Read access permitted in user mode
[bit10] UWE (User Mode Write Access Enable)
This bit is for enabling data write access in user mode for the specified protection area.
UWE
Access to the specified protection area
0
Write access not permitted in user mode (initial value)
1
Write access permitted in user mode
[bit9] Reserved
Always write "0" to this bit. This bit reads out "0".
[bit8] BE (Buffer Enable)
This bit permits buffering to be used during data access for the specified protection area. When the use of
buffering is forbidden, the CPU stops pipeline operation and waits for the data access to finish before
starting the next operation. As a result, although the data access efficiency decreases, it is possible to
perform data access synchronized to the instruction. Illegal instruction exceptions occur when there is an
error during data access only if buffering is forbidden. When buffering is permitted, data access errors can
be notified as interrupts.
BE
Bufferable specification for the specified protection area
0
Buffer Disable (Initial value)
1
Buffer Enable
[bit7 to bit3] ASZ[4:0] (Area Size)
These bits specify the size of the specified protection area. The specified address does not need to be
aligned to the sizes described below. Furthermore, if the lower limit of the area specified by the address and
size exceeds FFFFFFFF
H
, the lower limit of the area is treated as FFFFFFFF
H
.
ASZ[4:0]
Size of the specified
protectorate area
00000
B
Reserved
00001
B
Reserved
MB91520 Series
MN705-00010-1v0-E
139