User Manual

UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2010. All rights reserved.
User manual Rev. 2 — 19 August 2010 669 of 840
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
34.2.4.5 LDR, PC-relative
Load register from memory.
34.2.4.5.1 Syntax
LDR{type}{cond} Rt, label
LDRD{cond} Rt, Rt2, label ; Load two words
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.
Rt2 is the second register to load or store.
label is a PC-relative expression. See Section 34.2.3.6 “
PC-relative expressions”.
34.2.4.5.2 Operation
LDR loads a register with a value from a PC-relative memory address. The memory
address is specified by a label or by an offset from the PC.
The value to load or store can be a byte, halfword, or word. For load instructions, bytes
and halfwords can either be signed or unsigned. See Section 34.2.3.5 “
Address
alignment”.
label must be within a limited range of the current instruction. Table 618
shows the
possible offsets between label and the PC.
Remark: You might have to use the .W suffix to get the maximum offset range. See
Section 34.2.3.8 “
Instruction width selection”.
34.2.4.5.3 Restrictions
In these instructions:
• Rt can be SP or PC only for word loads
• Rt2 must not be SP and must not be PC
• Rt must be different from Rt2.
When Rt is PC in a word load instruction:
Table 618. Offset ranges
Instruction type Offset range
Word, halfword, signed halfword, byte, signed byte −4095 to 4095
Two words
−1020 to 1020