Memory Interface

Introduction

Simple or complex, every microprocessor-based system has

a memory system. 

Almost all systems contain two main types of memory:

read-only

memory

 (ROM) and

random access memory

(RAM) or read/write memory. 

This chapter explains how to interface both memory types to

the Intel family of microprocessors. 

 MEMORY DEVICES

Before attempting to interface memory to the

microprocessor, it is essential to understand the operation of

memory components. 

In this section, we explain functions of the

four common types of memory: 

read-only memory (ROM) 

Static random access memory (SRAM)

Memory Pin Connections 

address inputs

data outputs or

input/outputs

some type of

selection input

at least one control

input to select a read

or write operation

Address Connections

Memory devices have address inputs to

select a memory location within the device. 

Almost always labeled from A

0

, the least significant address

input, to A

where subscript n can be any value

always labeled as one less than total number

of address pins

A

memory device with 10 address pins has 

its address pins labeled from A

0

 to A

9

.

The number of address pins on a memory device is

determined by the number of memory locations found

within it.

Today, common memory devices have between 1K (1024)

to 1G (1,073,741,824) memory locations. 

with 4G and larger devices on the horizon