Page 229 - Mechatronics with Experiments

MICROCONTROLLERS 215

Brain
(CPU)
Clock

2 Cards
Right pocket Left pocket
(Acc. B) (Acc. A)

Black board Output Input Deck of cards
chalk eraser tray tray with details of
memory how to perform
(RAM) an instruction
(ROM)

FIGURE 4.3: Basic computer and human analogy.

(b) an instruction decoder register, which interprets the fetched instruction and passes
on the appropriate data to other registers,
(c) an arithmetic logic unit (ALU), which is the “brain inside the brain,” executes
the mathematical and logical operations.
2. A clock – a computer executes even the simplest instruction at the tick of a new clock
cycle. The clock is like the heart of a human body. Nothing happens in the computer
without the clock.
3. A ROM – read only memory which contains information on how to execute the basic
instruction set. It can only be read from and cannot be written to. It maintains data
when power is lost. EPROM is an erasable programmable ROM. An EPROM chip has
a window where the memory can be erased by exposing it to ultraviolet light and then
be reprogrammed. EEPROM is an electrically erasable programmable ROM where
the memory can be re-written by electrical signals in the communication interface
without any ultraviolet light.
4. RAM memory – random access memory serves as an erasable blackboard where the
information can be read from and written to. Data is lost if power is lost. Static RAM
and dynamic RAM are two common RAM types of memory. Static RAM stores data
in flip-flop circuits and does not require a refresh–write cycles to hold the data as
long as power is not lost. Dynamic RAM requires periodic refresh–write cycles to
hold the data even when power is maintained.
5. Registers are a few specific memory locations which can be accessed faster than the
other RAM memory locations.
6. I/O devices – every computer must interact with a user and external devices to perform
a useful function. It must be able to read in information from the outside world, process