Page 42 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Encoder
• It is a combinational circuit.
• It has ‘n’ input lines & ‘m’ output lines.

• An encoder produces an ‘m’ bit binary code corresponding to the digital input number of ‘n’bits.
• Many types of Encoders – Octal to Binary (8 to 3), Decimal to BCD (10 to 4)etc.
• The block diagram is as shown below,

Priority Encoder
• This is special type of encoder.

• Priorities are given to the input lines.
• Iftwoormoreinputlinesare‘1’at the same time, then the input line with highest priority will be considered.
• The block diagram is shown below

• The truth table of priority encoder is as given below,
• There are four inputs, D0 through D3 and outputs Y1 and Y0. Out of the four inputs D3 has the highest priority
and D0 has the lowest priority.

• That means if D3 = 1 then Y1Y0 = 11 irrespective of the other inputs. Similarly if D3 = 0 and D2 = 1 then Y1Y0
= 10 irrespective of other inputs
Truth Table

Inputs Outputs
D 3 D 2 D 1 D 0 Y 1 Y 0
0 0 0 0 X X
0 0 0 1 0 0
0 0 1 X 0 1
0 1 X X 1 0
1 X X X 1 1

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CITS : E & H - Electronics Mechanic - Lesson 9 - 29