ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Assembler syntax
LDRH , Normal form
LDRH , [PC, #+/-] Alternative form
where:
See Standard assembler syntax fields on page A8-7.
The destination register.
Instruction Details
The label of the literal data item that is to be loaded into . The assembler calculates the
required value of the offset from the Align(PC,4) value of the ADR instruction to this label.
Permitted values of the offset are:
Encoding T1 any value in the range -4095 to 4095
Encoding A1 any value in the range -255 to 255.
If the offset is zero or positive, imm32 is equal to the offset and add == TRUE.
If the offset is negative, imm32 is equal to minus the offset and add == FALSE.
The alternative syntax permits the addition or subtraction of the offset and the immediate offset to be
specified separately, including permitting a subtraction of 0 that cannot be specified using the normal
syntax. For more information, see Use of labels in UAL instruction syntax on page A4-5.
The pre-UAL syntax LDRH is equivalent to LDRH.
Operation
if ConditionPassed() then
EncodingSpecificOperations(); NullCheckIfThumbEE(15);
base = Align(PC,4);
address = if add then (base + imm32) else (base - imm32);
data = MemU[address,2];
if UnalignedSupport() || address = ‘0’ then
R[t] = ZeroExtend(data, 32);
else // Can only apply before ARMv7
R[t] = bits(32) UNKNOWN;
Exceptions
Data Abort.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. A8-155