5.5 LOGIC CIRCUIT
LOGIC SYSTEMS
• System performs calculation or makes decisions • A logical operation on one or more logic inputs
and produces a single logic output to make decision.
• Using electronic component that can conduct electricity based on a rule either analog or digital.
• Primarily implement using diodes or transistor acting as electronic switch
POSITIVE AND NEGATIVE LOGIC
OR GATE
X
X = A + B
A B X0 0 00 1 11 0 11 1 1
IF GOT 1 = RESULT MUST BE 1
AND GATE
X = A.B
A B X0 0 00 1 01 0 01 1 1
IF GOT 0 = RESULT MUST BE 0
NOT GATE
A X0 11 0
NAND GATE
A B X0 0 10 1 11 0 11 1 0
X
NOR GATE
A B X0 0 10 1 01 0 01 1 0
X
EXCLUSIVE OR GATE
A B X0 0 00 1 11 0 11 1 0X
EXCLUSIVE OR GATE
C B A X0 0 0 00 0 1 10 1 0 10 1 1 01 0 0 11 0 1 01 1 0 01 1 1 1
Any ODD number of Inputs gives X
X
EXCLUSIVE NOR GATE
A
BX
X
A B X0 0 10 1 01 0 01 1 1
GATE TABLE
A B OR NOR AND NAND EX-OR EX-NOR
NOT A
0 0 0 1 0 1 0 1 10 1 1 0 0 1 1 0 11 0 1 0 0 1 1 0 01 1 1 0 1 0 0 1 0
UNIVERSAL GATE
• NAND gate is universal gate• It can make another gate
NOT GATE
OR GATE
B
AND GATE
IC - INTEGRATED CIRCUIT
Quad 2-input AND Gate 7408
ADDERS
• An adder or summer is a digital circuit that performs addition of numbers.
• For new processor, adder are use to calculate addresses, table indices (database).
• The most common adders operate on binary numbers
HALF ADDER CIRCUIT
• Required 2 input and provide 2 output• Combination of an exclusive OR and an AND
gate
A B SUM CARRY0 0 0 00 1 1 01 0 1 01 1 0 1
SUM = A BCARRY = A . B
FULL ADDER CIRCUIT
• Required 3 input provide 2 output• Combination of 2 half adder and OR gate.
A B Cin Cout S0 0 0 0 01 0 0 0 10 1 0 0 11 1 0 1 00 0 1 0 11 0 1 1 00 1 1 1 01 1 1 1 1
INPUTS OUTPUTS
AIRCRAFT LOGIC CIRCUIT
• LANDING GEAR WARNING CIRCUIT
AIRCRAFT LOGIC CIRCUIT
• FLIGHT DIRECTOR GYRO FLAG - drop when gyro system malfunction either loss of vacuum or electrical signal
Error Flag
GYRO FLAG SYSTEM
SERVO ALTIMETER OFF FLAG• Correct operating when sin outputs (‘0’) and the cos
outputs (‘1’).• When total output is 1, it will energising the OFF Flag
coil, removing the flag from view.