Page 86 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

0
16 1 1 → MSB
16 27 11 or B
16 432 0 → LSB
[432] = [1B0] 16
10
Hexadecimal to Decimal
This conversion can be done by putting it into the positional notation.

Ex: 223A = 2 x 16 + 2 x 16 + 3 x 16 + A x 16 0
2
1
3
16
= 2 x 4096 + 2 x 256 + 3 x 16 + 10 x 1
= 8192 + 512 + 48 + 10
= 8762 10
BCD (Binary Coded Decimal)
Binary Coded Decimal (BCD) is a way to express each of the decimal digits with a binary code, since there are
only ten code groups in the BCD system, it is very easy to convert between decimal and BCD. Because decimal
system is used for read and write, BCD code provides an excellent interface to binary systems. Examples of such
interfaces are keypad inputs and digital readouts.
8421 code
The 8421 code is a type of binary coded decimal (BCD), binary coded decimal means that each decimal digit, 0
through 9 is represented by a binary code of four bits. The designation 8421 indicates the binary weights of the
four bits (2 , 2 , 2 , 2 ). The ease of conversion between 8421 code numbers and the familiar decimal numbers is
1
2
3
0
the main advantage of this code. All you have to remember are the ten binary combinations that represents the
ten decimal digits as shown in the Table.
Decimal 0 1 2 3 4
digit
BCD 0000 0001 0010 0011 0100

Decimal 5 6 7 8 9
digit
BCD 0101 0110 0111 1000 1001

The 8421 code is the pre-dominant BCD code, and when we refer to BCD, we always mean the 8421 code unless
otherwise stated.
Inverters (NOT Gate)
An inverter is a gate with only one input signal and one output signal. The output state is always the opposite of
the input state. Logic symbol is shown in Fig 1.
Transistor inverter
The Fig 2 shows the transistor inverter circuit. The circuit is a common emitter amplifier which works in saturation
or in cut off region depending upon the input voltage. When Vin is in low level, say less than the transistor cut in
voltage 0.6V in silicon type, the transistor goes to cut off condition and the collector current is zero. Therefore,
Vout = +5V which is taken as high logic level. On the other hand, when Vin is in high level, the transistor saturates
and Vout = Vsat = 0.3V i.e low level.
The table summarizes the operation

V in V out
Low(0) High(1)
High(1) Low(0)

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CITS : Power - Electrician & Wireman - Lesson 60-69