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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
742 of 808
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 User Guide
4.3.6.1
Binary point
The PRIGROUP field indicates the position of the binary point that splits the PRI_
n
fields
in the Interrupt Priority Registers into separate
group priority
and
subpriority
fields.
shows how the PRIGROUP value controls this split.
[1]
PRI_
n
[7:0] field showing the binary point. x denotes a group priority field bit, and y denotes a subpriority field bit. Bits [2:0] are not used
in LPC17xx devices.
Remark:
Determining preemption of an exception uses only the group priority field, see
Section 35–1.3.6 “Interrupt priority grouping”
4.3.7 System Control Register
The SCR controls features of entry to and exit from low power state. See the register
summary in
for its attributes. The bit assignments are shown in
[2]
SYSRESETREQ
WO
System reset request:
0 = no system reset request
1 = asserts a signal to the outer system that requests a
reset.
This is intended to force a large system reset of all major
components except for debug.
Note: support for
SYSRESETREQ is not included in LPC17xx devices.
This bit reads as 0.
[1]
VECTCLRACTIVE
WO
Reserved for Debug use. This bit reads as 0. When writing
to the register you must write 0 to this bit, otherwise
behavior is Unpredictable.
[0]
VECTRESET
WO
Reserved for Debug use. This bit reads as 0. When writing
to the register you must write 0 to this bit, otherwise
behavior is Unpredictable.
Table 631. AIRCR bit assignments
Bits
Name
Type
Function
Table 632. Priority grouping
Interrupt priority level value, PRI_N[7:0]
Number of
PRIGROUP
Binary point
Group priority
bits
Subpriority bits
Group priorities
Subpriorities
b010
bxxxxxy000
[7:3]
none
32
1
b011
bxxxx.y000
[7:4]
[3]
16
2
b100
bxxx.yy000
[7:5]
[4:3]
8
3
b101
bxx.yyy000
[7:6]
[5:3]
4
8
b110
bx.yyyy000
[7]
[6:3]
2
16
b111
b.yyyyy000
None
[7:3]
1
32