LDRB - Load Register Byte

Syntax

LDR[condition]B dest, addr_mode

where:

condition	One of 16 conditions. Refer to Condition Code Status.
dest	destination register
addr_mode	Addressing Mode 2: Load and Store Word or Unsigned Byte

Description

The LDRB instruction loads a byte from addr_mode into dest . This byte is zero-extended into a 32-bit word enabling 8-bit memory data to be manipulated. It also enables PC-relative addressing if used as a base register. The condition needs to be a valid value; else the instruction is rendered an NOP.

Note

A data abort exception is generated if an invalid load or store data access is attempted.

Addressing Mode

See Addressing Mode 2: Load and Store Word or Unsigned Byte

Flags Affected

N	Z	C	V	Q	S	I	F	T
T	T	T	T

Encoding

31		28	27	26	25	24	23	22	21	20	19		16	15		12	11		0
condition			0	1	I	P	U	1	W	1	basereg			dest			addr_mode

Example

1                      @.text
2                      @.globl funcldrb
3                      @.align 0
4
5                      @ * * * LDRB (Addressing Mode 2) * * *
6                  AREA load_store, CODE, READONLY
7                  label1
8    00000000   E3A0B001   MOV   R11, #1
9    00000004   E2AB0001   ADC   R0, R11, #1
00000008   E4507000   LDRB R7, label2
11
12   00000012   E12FFF17   BXR7
13
14   00000016   E3A0B001   MOV   R11, #1
15   00000020   E21B0001   ANDS R0, R11, #1
16
17   00000024   E3A0000A   MOV   R0, #10
18   00000028   E3A01001   MOV   R1, #1
19   00000032   E5801000   STR   R1, [R0]
20   00000036   E5D02000   LDRB R2, [R0]
21
22                         END
23
24                 label2
25                         DCD   0xdeadbeef
26                         DCB   "string"
27
28                         END

Further Information

See Addressing Mode 2: Load and Store Word or Unsigned Byte