Digital Signal Processing Reference
In-Depth Information
9 A Simple Computer Design: The µP 3
A traditional digital computer consists of three main units, the processor or
central processing unit (CPU), the memory that stores program instructions and
data, and the input/output hardware that communicates to other devices. As
seen in Figure 9.1, these units are connected by a collection of parallel digital
signals called a bus. Typically, signals on the bus include the memory address,
memory data, and bus status. Bus status signals indicate the current bus
operation, memory read, memory write, or input/output operation.
Processor
Memory
Input/Ouput
PC
IR
AC
Address Bus
MAR
Data Bus
ALU
MDR
Control
Unit
Figure 9.1
Architecture of a Simple Computer System.
Internally, the CPU contains a small number of registers that are used to store
data inside the processor. Registers such as PC, IR, AC, MAR and MDR are
built using D flip-flops for data storage. One or more arithmetic logic units
(ALUs) are also contained inside the CPU. The ALU is used to perform
arithmetic and logical operations on data values. Common ALU operations
include add, subtract, and logical and/or operations. Register-to-bus
connections are hard wired for simple point-to-point connections. When one of
several registers can drive the bus, the connections are constructed using
multiplexers, open collector outputs, or tri-state outputs. The control unit is a
complex state machine that controls the internal operation of the processor.
The primary operation performed by the processor is the execution of
sequences of instructions stored in main memory. The CPU or processor reads
or fetches an instruction from memory, decodes the instruction to determine
what operations are required, and then executes the instruction. The control unit
controls this sequence of operations in the processor.
