Logic Circuits Flashcards
what types of logic gates are there
AND, OR, NOT,NOR,NAND,XOR,XNOR
What is an IC/”gate”
an electronic circuit that is constructed entirely on a single small chip of silicone
What is a Dual In Line package (DIP)
a type of electronic chip with 2 rows of pins
what is a fixed function logic
a category of digital integrated circuits having functions that cannot be altered
what is programmable logic
a category of integrated circuits capable of being programmed to perform specific functions
what is an ‘inverter’
performs the boolean NOT operation (X = ~ A)
- input is HIGH, output is LOW and vise versa
what is the ‘AND’ gate
X = A.B or X = AB
produces a HIGH output when all inputs are high
what is the ‘OR’ gate
X = A+B
produces HIGH output if any input is HIGH
- if all inputs are LOW, output is LOW
what is the ‘NAND’ gate
X = A.B (bar on top) = AB (bar)
produces LOW output when all inputs are HIGH, otherwise all output is HIGH
- universal gate
what is a ‘NOR’ gate
X = A + B (bar)
produces a LOW output if any input is HIGH
All HIGH = LOW
All LOW = HIGH
what is a ‘XOR’ gate
X = A(bar)B + AB(bar)
output is HIGH if inputs are different
what is a “XNOR” gate
X = AB bar + AB
produces a HIGH output if inputs are the same logic level
what is a complement
the inverse of a variable & is indicated with an overbar
what is a literal
a variable or its complement
what IC is used for Boolean addition
OR operation
what IC is used for Boolean multiplication
AND operation
How does the variable order affect the addition commutative laws
no difference
How does the variable order affect the multiplication commutative laws
no difference
How does the variable order affect the addition associative laws
when OR-ing more than 2 variables, the result is the same regardless of how it has been grouped
How does the variable order affect the multiplication associative laws
when AND-ing more than 2 variables, the result is the same regardless of how it has been grouped
what is DeMorgans 1st theorem
the complement of a product of variables is equal to the sum of the complemented variables
AB bar = A bar + B bar
what is DeMorgans 2nd theorem
the complement of a sum of variables id equal to the product of the complemented variables
A + B (BAR) = A bar . B bar
what occurs if a variable has 2 overbars
cancel out
A double bar = A
what is a karnaugh map
a tool for simplifying combinational logic
- simplify combinational logic by grouping cells and eliminating variables that change
what is combinational logic
whose output is a function of only present inputs
what is sequential logic
whose output is a function of present and past inputs
what is XOR gate logic
if inputs disagree, output are HIGH
what is XNOR gate logic
if inputs agree, output is HIGH
What Variables have a 0 logic level value
A bar, B bar, C bar, D bar
What Variables have a 1 logic level value
A, B, C, D
How can you implement SOP expressions
Form the AND terms, Then OR the terms together
what can multiple NAND gates do?
1 = inverter
2 = AND operation
3 = OR operation
4 = NOR operation
what can multiple NOR gates do?
1 = inverter
2 = OR operation
3 = AND operation
4 = NAND operation
what is a half adder
a digital circuit that performs binary addition of 2 one bit inputs and has two outputs of sum and carry out
what is a full adder
digital circuit that performs binary addition of three bits ( 2 inputs and a carry In) and produces a sum and a carry-out bit (sum and carry out)
what are parallel adders
full adders that are combined that can add binary numbers with multiple bits
what are comparators
a device that compares the magnitudes of 2 binary numbers to determine the relationship between them
function of IC comparators
provide outputs to indicate which of the numbers is larger or if they are equal
function of decoders
a logic circuit that detects the presence of a specific combination of bits at its input
function of encoders
accepts an active logic level on one of its inputs and converts it to a coded output (BCD or Binary)
function of a multiplexer
selects one data line from two or more input lines and routes data from the selected line to the output
function of the demultiplexers
switches data from one input line to two or more data lines depending on the select inputs
what are latches
a temporary storage device that has 2 stable states
what is an S-R latch
Set Reset Latch
- can be made from NOR gate
- responds to active HIGH inputs
what are the input rules of an SR latch
R = 0, S = 1 : latch RESET
R = 1, S = 0 = : latch SET
Both 1 : invalid
Both 0 : no change
How is a SR active-high latch made stable
both inputs are low
How is the SR active-high latch SET
a momentary HIGH signal is applied to the S input whilst R remains low
How is the SR active-high latch RESET
a momentary HIGH signal is applied to the R input whilst S remains low
How does a NAND constructed SR latch differ from a NOR constructed SR latch
latch responds to active-low inputs
How is a SR active-low latch made stable
when both inputs are high
How is the SR active-low latch SET
a momentary LOW signal is applied to the S bar input whilst R bar remains high
How is the SR active-low latch RESET
a momentary LOW signal is applied to the R bar input whilst S bar remains high
what is the Enable (EN) input
input within the gated SR latch that must be HIGH in order for the latch to respond to the S & R inputs
what is a D latch
variation of the SR latch that combines the S & R inputs into a single D input
- Q follows D when enable is active
What are flip flops
a clocked device, in which only the clock edge determines when a new bit is entered
- can be positive or negative edged
what is a toggle
changes output until device becomes set again
