Memory is part of the
microcontroller used
for data storage.
The easiest way to explain it is to compare it with a filing cabinet with
many drawers.
Suppose, the drawers are clearly marked so that it is easy to access any of
them. It is easy enough to find out the contents of the drawer by reading the
label on the front of the drawer.
Each memory address
corresponds to one memory location. The content of any location becomes known
by its addressing. Memory can either be written to or read from. There are
several types of memory within the microcontroller.
Read Only Memory (ROM)
ROM (Read Only
Memory) is used to
permanently save the program being executed. The size of a program that can be
written depends on the size of this memory. Today’s microcontrollers commonly
use 16-bit addressing, which
means that they are able to address up to 64 Kb of memory, i.e. 65535 locations. As a novice, your program will rarely exceed the limit
of several hundred instructions. There are several types of ROM.
Masked ROM
Microcontrollers
containing this ROM are reserved for the great manufacturers. Program is loaded into the chip by the
manufacturer.
One Time Programmable ROM (OTP ROM)
If the
microcontroller contains this memory, you can download a program into this
memory, but the process of program downloading is a “one-way ticket”, meaning
that it can be done only once. If an error is detected after downloading, the
only thing you can do is to download the corrected program
to another chip.
UV Erasable Programmable ROM (UV EPROM)
Both the manufacturing process
and characteristics
of this memory are completely identical to OTP ROM.
However, the package of this microcontroller has a recognizable “window” on the
upper side. It enables the surface of the silicon chip inside to be lit by an
UV lamp, which effectively erases and program from the ROM. Installation of
this window is very complicated, which normally affects the price. From our
point of view, unfortunately- negative...
Flash memory
This type of memory
was invented in the 80s in the laboratories of INTEL and were represented as
the successor to the UV EPROM. Since the contents of this memory can be written and cleared
practically an unlimited number of times, the microcontrollers with Flash ROM are ideal for
learning, experimentation and small-scale manufacture. Because of its
popularity, the most microcontrollers are manufactured in flash versions today.
So, if you are going to buy a microcontroller, the type to look for is
definitely Flash!
Random Access Memory (RAM)
Once the power supply is
off the contents of RAM (Random Access
Memory) is cleared.
It is used for temporary
storing data and intermediate results created and used during the operation of the
microcontroller. For example, if the program performs an addition (of
whatever), it is necessary to have a register representing what in everyday
life is called the “sum”. For that purpose, one of the registers in RAM is
called the “sum” and used for storing results of addition.
Electrically Erasable Programmable ROM (EEPROM)
The contents of the EEPROM may be changed
during operation (similar
to RAM), but remains permanently saved even upon the power supply goes off (similar to ROM).
Accordingly, an EEPROM is often used to store values, created during operation,
which must be permanently saved. For example, if you design an electronic lock
or an alarm, it would be great to enable the user to create and enter a password,
but useless if it is lost every time the power supply goes off. The ideal
solution is the microcontroller with an embedded EEPROM.
Cheers!!!!
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