Wednesday, June 18, 2008

Dont care condition

Don’t Care Conditions
1) Don’t Care conditions only arise during design, they are never present as a result of analysis
Why? Once the circuit is built the output is always either 0 volts or 5 volts -- a logical “1” or a logical “0”.
There are NOT 3 outputs: 0 volts, 5 volts, and don’t care volts
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Applications of Decoder

1. It is now used in most wireless control system.
2.In the Television receiver,the original image is reconstructed essentially by reversing the operation of the video dishes to receive signals directly from satellites.
3.Most satellite delivered signals are scrambled and require a special decoder to receive them clearly

FLIP FLOP

Flip-Flops
"Flip-flop" is the common name given to two-state devices which offer basic memory for sequential logic operations. Flip-flops are heavily used for digital data storage and transfer and are commonly used in banks called "registers" for the storage of binary numerical data.

REFER THE FOLLOWING LINK FOR DETAILED DISCRIPTION :
http://hyperphysics.phy-astr.gsu.edu/Hbase/electronic/flipflop.html#c2

dont care condition

When the input can never occur
If an input can never occur, a don’t care can be used during design
An example is when BCD (binary coded decimal) is used to represent numbers. That is each decimal digit is represented by 4 bits (0 =0000, 1 = 0001, …, 9 = 1001).
Thus each decimal digit requires 4 bits but only 10 of the 16 possible combinations are used. Thus the outputs for inputs 1010, 1011, … , 1111 can be specified as don’t cares.
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Dont Care Condition

1.They represent the degrees of freedom of transforming a network in to an equivalent one.
2.We would not normally care to fill in the codes(1010,1011,1100,1101,1110,1111)because these codes will never exist as long as we are dealing only with BCD encoder numbers.These six invalid codes are dont cares