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
