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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
636 of 808
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 User Guide
2.4.4 LDR and STR, unprivileged
Load and Store with unprivileged access.
2.4.4.1
Syntax
op
{
type
}T{
cond
}
Rt
, [
Rn
{, #
offset
}]
; immediate offset
where:
op
is one of:
LDR
: Load Register.
STR
: Store Register.
type
is one of:
B
: unsigned byte, zero extend to 32 bits on loads.
SB
: signed byte, sign extend to 32 bits (
LDR
only).
H
: unsigned halfword, zero extend to 32 bits on loads.
SH
: signed halfword, sign extend to 32 bits (
LDR
only).
—: omit, for word.
cond
is an optional condition code, see
Section 34–2.3.7 “Conditional execution”
.
Rt
is the register to load or store.
Rn
is the register on which the memory address is based.
offset
is an offset from
Rn
and can be 0 to 255. If
offset
is omitted, the address is the value
in
Rn
.
2.4.4.2
Operation
These load and store instructions perform the same function as the memory access
instructions with immediate offset, see
. The difference is that these
instructions have only unprivileged access even when used in privileged software.
When used in unprivileged software, these instructions behave in exactly the same way
as normal memory access instructions with immediate offset.
2.4.4.3
Restrictions
In these instructions:
•
Rn
must not be PC
•
Rt
must not be SP and must not be PC.
2.4.4.4
Condition flags
These instructions do not change the flags.