Notation: Rt, Rn denote ARM registers R0-R7 except where stated. immN represents an immediate value having a width of N bits hence imm5 is constrained to the range 0-31. [Rn + immN] is the contents of the memory address obtained by adding Rn and the offset immN. Offsets are measured in bytes. These instructions affect the condition flags.
- ldr(Rt, [Rn, imm7])
Rt = [Rn + imm7]Load a 32 bit word - ldrb(Rt, [Rn, imm5])
Rt = [Rn + imm5]Load a byte - ldrh(Rt, [Rn, imm6])
Rt = [Rn + imm6]Load a 16 bit half word
Where a byte or half word is loaded, it is zero-extended to 32 bits.
The specified immediate offsets are measured in bytes. Hence in the case of ldr the 7 bit value enables 32 bit word aligned values to be accessed with a maximum offset of 31 words. In the case of ldrh the 6 bit value enables 16 bit half-word aligned values to be accessed with a maximum offset of 31 half-words.