Combinational and Sequential Logic LOGIC DEVICES TOM FAULKNER
History
Digital Logic was first outlined by George Boole in his theory of Boolean Logic
This principle works on three parts, AND, OR and NOT
Digital Logic first came into play in the 1940’s, beginning as large, hot, power hungry ‘dual triode’ vacuum tubes, which could store up to one bit of data each.
To put this in perspective, today we have hard drives that can store up to one terabyte of data (and even more), which is equivalent to 8 x10^12 bits.
The Age of Semiconductors
After years of attempting to develop components that were better suited to logic devices, the semiconductor was developed in 1947.
After some initial tests using transistors made using germanium (a rare earth metal), it was decided to use silicon to make them.
The space race in 1957 increased the demand for semiconductors, and the launch of Sputnik 1 on October 4th, 1957 was the catalyst needed to accelerate the development of semiconductors exponentially.
This eventually resulted in the creation of the so called ‘Silicon Valley’ that we know today.
Microcontrollers
A microcontroller is a common digital electronic device used in many different pieces of equipment, belonging to the CMOS family.
The first Microcontroller was created in the 1970’s by a company called ‘Intel’.
The microcontroller takes components from a system and incorporates them onto a single chip. They contain (simply) a CPU core, memory and the same I/O used in microprocessors.
They can use RAM (Random Access Memory) and ROM (Read-Only Memory), although the ROM can be substituted for EEPROM, which is a type of memory which can be electronically erased and reprogrammed to carry out a different purpose.
Uses of Microcontrollers ď ľ
Microcontrollers can be applied in a number of situations. A common use for them is in the control of anti- lock brakes. The microcontroller that carries out this function is often found in a cars ECU.
Crystal Oscillators ď ľ
A crystal oscillator is an electronic component that uses a vibrating piece of piezoelectric crystal that generates an electrical signal dependant on the type of vibration (or pressure) that is applied to it.
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They create signals with a very precise frequency, which can be applied to highprecision tasks, such as keeping track of time.
Uses of Crystal Oscillators
A common use in electronics for a crystal oscillator is an oscilloscope, which displays waveforms.
Simply, it draws a graph of an electrical waveform. Through looking at this graph, you can calculate the time base, frequency and voltage of a particular waveform.
It can also be used for fault finding, as you should be able to tell through examining the waveform whether a malfunctioning component is altering the signal.
Logic Families
The two most common logic ‘families’ used are CMOS (Complementary MetalOxide-Semiconductor) and TTL (Transistor-Transistor Logic).
CMOS uses positive polarity and negative polarity circuits in conjunction with each other. However, each circuit only operates at a given time (one at once) which means that these components use less power than TTL components.
TTL components use ‘bipolar transistors’ to operate, and these require higher levels of power to operate. They require between 0-0.8V to produce a ‘logic 0’, and between 2V-5V to produce a ‘logic 1’.
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