First generation: 1971-78
Behind the power curve
(16-bit, <50k transistors)
Second Generation: 1979-85
Becoming “real” computers
(32-bit , >50k transistors)
Third Generation: 1985-89
Challenging the “establishment”
(Reduced Instruction Set Computer/RISC,
Fourth Generation: 1990-
Architectural and performance leadership
(64-bit, > 1M transistors,
Intel/AMD translate into RISC internally)
Focus on microprocessors as general purpose,
flexible and reconfigurable controllers and the ways
sensors and actuator relate to these.
Microprocessors are often called microcontrollers
What is a microprocessor? What is the different
between a microprocessor and a computer or a
microcomputer and how a distinguishing set of
features is arrived at are all difficult and subjective
issues. What is a microprocessor to one is a full
fledged computer to another
microprocessor is a stand alone, self contained single
It must have as a minimum:
a central processing unit (CPU)
nonvolatile and program memory
input and output capabilities.
A structure that has these can be programmed in some
convenient programming language
can interact with the outside world through the
• Other important requirements:
• must be relatively simple
• reasonably small
• necessarily limited in most of its features – memory,
processing power and speed, addressing range and, of
course in number of I/O devices it can interact with.
• The designer must have access to all features of the
microprocessor – bus, memory, registers, all I/O ports,
• In short, Microprocessors are components with
flexible features that the engineer can configure and
program to perform task or a series of tasks.
• Two limits on the tasks microprocessors can perform:
• The limitations of the microprocessor itself
• The imagination (or capabilities) of the designer.
The 8 bit microprocessor
We will narrow down to 8 bit microprocessors
these are the most common in sensor/actuator systems
they are simple and representative of all microprocessor
16 and 32 bit microprocessors exist
There are a number of architectures being used.
We will emphasize the Harvard architecture because
of its simplicity, flexibility and popularity.
8 bit microprocessors have word length of 8 bits.
Integer data from 0 to 255 may be represented directly.
To address memory, usually a longer word is needed.
Most microprocessor have a 12 bit (4k) 14 (16k) or 16 bit
(64k) memory address but longer address words are also
Most microprocessor operate at clock speeds between 1
and 40 MHz.
Since often the clock is internally divided, the instruction
cycle is slower than that
Typical values are up to about 10 MHz cycle clock or 0.1
µs per instruction
Input and output
Input and output is defined by the availability of pins
on the package.
Usually limited to less than about 100 pins (6, 8, 14,
18, 20, 28, 32, 40, 44, 64 and 100 pins are common).
Two pins are used to power to the device
For example, an 18 pin device can have no more than
14 I/O pins.
Of these, some may be used for other purposes such
as oscillators or communication
Clock and timers
Microprocessors have internal timers
under the control of the user
used for various functions requiring counting/timing
At least one counter is available
larger microprocessors can have 4 or more timers
some are 8 bit timers and some 16 bit timers.
a watchdog timer is available for the purpose of resetting
the processor should it be “stuck” in an inoperative mode.
• Many microprocessors provide multiple interfaces, all
under the user’s control.
• Other functions such as analog amplifiers and even
transceivers are sometimes incorporated within the chip.
• The I/O used for these functions are either digital I/O (for
communication for example) or analog
Programs and programmability
microprocessor is only useful if it can be
Programming languages and compilers have been
designed specifically for microprocessors.
The basic method of programming microprocessors is
through the Assembly programming language
Can be, and very often is done through use of higher
level languages with C leading.