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2 - How does a typical microcontroller work?
Table 1. Table of the main processor sizes
Relative
power
Data size
Common applications
4 bits
Lowest
Watches, calculators, TV remote control, washing machines.
8 bits
Low
Industrial products and home computers in the ’80s; most
microcontrollers today where little numeric computation is required.
16 bits
Medium
As a microprocessor, the former PCs; as a microcontroller,
industrial and automotive products used in car bodies.
32 bits
High
All PCs use this size of microprocessor today; some
microcontrollers are also becoming available commercially such as
automotive injection calculators.
64 bits
Highest
Only in mainframes; microcontrollers of this size are just coming out
from the laboratories.
2.2 HOW THE CPU AND ITS PERIPHERALS MAKE UP A SYSTEM
The CPU cannot work alone. It is the central piece of a system that includes the following components:
2.2.1 CPU
It computes and coordinates. It controls almost all the other components of the system, except
in some cases like interrupts or direct memory access where some peripherals take the initiative.
2.2.2 Memory
It stores both the program, that tells the CPU what to do, and the data, that is temporarily
stored by the CPU like intermediate computation results, and the global state of the system.
■
In computers, there is only one memory to store both. This memory is volatile, so that a
supplementary, high-capacity and non-volatile storage is required to hold the contents of the
memory when the system is not powered-on, in most cases a hard magnetic disk. The cost
per bit stored of the memory being much higher than that of the hard disk, the capacity of the
memory is usually much lower than that of the disk. Only a fraction of the disk contents
resides in memory at any time.
■
In microprocessor-based systems, the memory is the only storage, and various types of
memory are used according to its use: read-only memory for the program, read-write
memory for the data, and/or non-volatile solid-state memory for those data that must be
preserved from one session to the next, the system being powered-off between two
sessions.
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