ARM7TDMI データシートの表示（PDF） - Unspecified

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ARM7TDMI

General-Purpose 32-Bit Microprocessors

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Introduction

1.2 Architecture

The ARM7TDMI processor has two instruction sets:

• the 32-bit ARM instruction set

• the 16-bit Thumb instruction set.

The ARM7TDMI processor is an implementation of the ARMv4T architecture. For full

details of both the ARM and Thumb instruction sets refer to the ARM Architecture

Reference Manual.

This section describes:

• Instruction compression on page 1-5

• The Thumb instruction set on page 1-5.

1.2.1

Instruction compression

Microprocessor architectures traditionally had the same width for instructions, and data.

Therefore 32-bit architectures had higher performance manipulating 32-bit data, and

could address a large address space much more efficiently than 16-bit architectures.

16-bit architectures typically had higher code density than 32-bit architectures, but

approximately half the performance.

Thumb implements a 16-bit instruction set on a 32-bit architecture to provide:

• higher performance than a 16-bit architecture

• higher code density than a 32-bit architecture.

1.2.2

The Thumb instruction set

The Thumb instruction set is a subset of the most commonly used 32-bit ARM

instructions. Thumb instructions are each 16 bits long, and have a corresponding 32-bit

ARM instruction that has the same effect on the processor model. Thumb instructions

operate with the standard ARM register configuration, allowing excellent

interoperability between ARM and Thumb states.

On execution, 16-bit Thumb instructions are transparently decompressed to full 32-bit

ARM instructions in real time, without performance loss.

Thumb has all the advantages of a 32-bit core:

• 32-bit address space

• 32-bit registers

• 32-bit shifter, and Arithmetic Logic Unit (ALU)

• 32-bit memory transfer.

ARM DDI 0029G

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