Logic Diagrams Truth Tables
o Logic gates are Boolean operations of three types - AND, OR & NOT. o Inputs and outputs from gates and logic circuits can be written in truth tables where all
o NOT gate - input 0 (no current supplied), output 1 (electrical current possible inputs are noted together with the output.
supplied) - reverses the input.
o AND gate - two inputs where both need to be on (1 and 1 input gives an
electrical current) in order to output 1
o OR gate - two inputs where either of the inputs can be on (or both) for the
output to be on (0 and 1 input will output 1)
o Logic gates can be combined to produce a logic diagram.
D = (A AND B) OR NOT C D = NOT (C AND (A OR B)) / D = NOT ((A AND B) AND C) D = (A OR B) AND NOT C / D = NOT C AND (A OR B)
o eg. Fire alarm goes off if either (OR):
• The temp in a building rise above 60
degrees Celsius
• Someone manually sets off the fire alarm
o A fire officer should be able to manually shut off
the fire alarm regardless of the previous
circumstances (NOT).
o To convert a logic diagram into a truth table, add
a column for each beginning value and add
columns for the result of each logic gate and the
final outcome, then place all possible outcomes of
the beginning values and work out the rest from
there.
o Logic gates are Boolean operations of three types - AND, OR & NOT. o Inputs and outputs from gates and logic circuits can be written in truth tables where all
o NOT gate - input 0 (no current supplied), output 1 (electrical current possible inputs are noted together with the output.
supplied) - reverses the input.
o AND gate - two inputs where both need to be on (1 and 1 input gives an
electrical current) in order to output 1
o OR gate - two inputs where either of the inputs can be on (or both) for the
output to be on (0 and 1 input will output 1)
o Logic gates can be combined to produce a logic diagram.
D = (A AND B) OR NOT C D = NOT (C AND (A OR B)) / D = NOT ((A AND B) AND C) D = (A OR B) AND NOT C / D = NOT C AND (A OR B)
o eg. Fire alarm goes off if either (OR):
• The temp in a building rise above 60
degrees Celsius
• Someone manually sets off the fire alarm
o A fire officer should be able to manually shut off
the fire alarm regardless of the previous
circumstances (NOT).
o To convert a logic diagram into a truth table, add
a column for each beginning value and add
columns for the result of each logic gate and the
final outcome, then place all possible outcomes of
the beginning values and work out the rest from
there.
