ARMv1 is the first ARM instruction set version. Introduced with the ARM1 on April 26 1985, the ARMv1 defines a 32-bit ISA along with 26-bit addressing space. The ARMv1 was only implemented by the ARM1 and was replaced soon after by the ARM2. Only a few hundred of those chips were ever fabricated.

Overview

The ARMv1 is a simple architecture. Each instruction is 32-bit in size and operates on two 32-bit operands. There is a program counter which is 26 bits in size allowing for an address space of up to 64 MiB of data.

Registers

There are 16 general purpose 32-bit registers. With the exception of register 15, all registers are orthogonal with no specific designated purpose.

Instruction Listing

The ARMv1 is broken down into 2 classes of instruction:

• Load Instructions
• Store Instructions

ARMv1 ISA
Mnemonic	Syntax	Description	Action
Load Instructions
LDR	LDR{cond} Rd, address	Load Word	Rd = [address]
LDRT	LDRT{cond} Rd, address	Load Word, User Mode Privilege	Rd = [address]
LDRB	LDRB{cond} Rd, address	Load Byte	Rd = ZeroExtend([address])
LDRBT	LDRBT{cond} Rd, address	Load Byte, User Mode Privilege	Rd = ZeroExtend([address])
LDM	LDM{cond}{type} Rn[!], {reglist}	Load Multiple	addr = Rn for each Rd in {reglist}:      Rd = [addr]      addr += {type}
LDM	LDM{cond}{type} Rn[!], {reglist, PC}	Load Multiple	addr = Rn for each Rd in {reglist}:      Rd = [addr]      addr += {type} R15 = [addr]
Store Instructions
STR	STR{cond} Rd, address	Store Word	[address] = Rd
STRT	STRT{cond} Rd, address	Store Word, User Mode Privilege	[address] = Rd
STRB	STRB{cond} Rd, address	Store Byte	[address][7:0] = Rd[7:0]
STRBT	STRBT{cond} Rd, address	Store Byte, User Mode Privilege	[address][7:0] = Rd[7:0]
STM	STM{cond}{type} Rn[!], {reglist}	Store Multiple	addr = Rn for each Rd in {reglist}:      [addr] = Rd      addr += {type}
STM	STM{cond}{type} Rn[!], {reglist}^	Store Multiple, User Mode Privilege	addr = Rn for each Rd in {reglist}:      [addr] = Rd      Rn += {type}