Introduction
1.1
Introduction
The ARM7TDMI is a member of the Advanced RISC Machines (ARM) family of
general purpose 32-bit microprocessors, which offer high performance for very low
power consumption and price.
The ARM architecture is based on Reduced Instruction Set Computer (RISC)
principles, and the instruction set and related decode mechanism are much simpler
than those of microprogrammed Complex Instruction Set Computers. This simplicity
results in a high instruction throughput and impressive real-time interrupt response
from a small and cost-effective chip.
Pipelining is employed so that all parts of the processing and memory systems can
operate continuously. Typically, while one instruction is being executed, its successor
is being decoded, and a third instruction is being fetched from memory.
The ARM memory interface has been designed to allow the performance potential to
be realised without incurring high costs in the memory system. Speed-critical control
signals are pipelined to allow system control functions to be implemented in standard
low-power logic, and these control signals facilitate the exploitation of the fast local
access modes offered by industry standard dynamic RAMs.
Open Access
1.2
ARM7TDMI Architecture
The ARM7TDMI processor employs a unique architectural strategy known as
THUMB
,
which makes it ideally suited to high-volume applications with memory restrictions, or
applications where code density is an issue.
1.2.1 The THUMB Concept
The key idea behind THUMB is that of a super-reduced instruction set. Essentially, the
ARM7TDMI processor has two instruction sets:
•
•
the standard 32-bit ARM set
a 16-bit THUMB set
The THUMB set’s 16-bit instruction length allows it to approach twice the density of
standard ARM code while retaining most of the ARM’s performance advantage over a
traditional 16-bit processor using 16-bit registers. This is possible because THUMB
code operates on the same 32-bit register set as ARM code.
THUMB code is able to provide up to 65% of the code size of ARM, and 160% of the
performance of an equivalent ARM processor connected to a 16-bit memory system.
1-2
ARM7TDMI Data Sheet
ARM DDI 0029E
ETC [ ETC ]
