Page 86 - Electrician - TT (Volume 2)
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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
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