# Combinational Circuits – Exercise – 1

Exercise – 1

1. An output of combinational circuit depends on : (a) Present inputs (b) Previous inputs (c) Both present and previous (d) None of above

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2. Half adder is an example of : (a) Combinational Circuits (b) Sequential Circuits (c) Asynchronous Circuits (d) None of these

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3. The relation between the number of inputs (n) and output (O) of binary code decoder is : (a) O = 2n (b) O =  2n (c) O = n+2 (d) O = n/2

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4. How many inputs are required for a 1 to 10 BCD decoder ? (a) 1 (b) 4 (c) 8 (d) 10

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5. A logic circuit which is used to change a BCD number into an equivalent decimal number is : (a) encoder (b) decoder (c) multiplexer (d) code converter

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• 555555555513. A multiplexed display: (a) accepts data inputs from one line and passes this data to multiple output lines (b) uses one display to present two or more pieces of information (c) accepts data inputs from multiple lines and passes this data to multiple output lines (d) accepts data inputs from several lines and multiplexes this input data to four BCD lines
• 555555555551. The RAM circuit given below is suspected of being bad. A check with a logic probe shows pulse activity on all of the address lines and data inputs. The / line and inputs are forced HIGH and the data output lines are checked with the logic probe. Q0, Q2, and Q3 show a dim indication on the logic probe; Q1 indicates a HIGH level on the logic probe. What, if anything, is wrong with the circuit? (a) The Q0, Q2, and Q3 output lines are open; the chip is defective. (b) The Q1 line appears to be shorted to Vcc; replace the chip. (c) The outputs should be active only when the / line is held LOW, so the circuit is behaving normally considering the fact that the line is HIGH. (d) The EN input should be forced HIGH and the outputs rechecked; if they are still giving the same indications as before, then the three outputs are definitely open and the IC will have to be replaced.
• Combinational Circuits » IQ - 1 1. Define combinational logic ? When logic gates are connected together to produce a specified output for certain specified combinations of input variables, with no storage involved, the resulting circuit is called combinational logic. 2. Explain the design procedure for combinational circuits ? (1) The problem definition. (2) Determine the number of available input variables & required O/P variables. (3) Assigning letter symbols to I/O variables. (4) Obtain simplified Boolean expression for each O/P. (5) Obtain the logic diagram. 3. Define multiplexer ? Multiplexer is a digital switch. If allows digitalinformation from several sources to be routed onto a single output line. 4. Define Decoder ? A decoder is a multiple - input multiple output logic circuit that converts coded inputs into coded outputs where the input and output codes are different. 5. What is binary decoder ? A  decoder is a combinational circuit that converts binary information from n input lines to a maximum of 2n out puts lines. 6. Define Encoder ? An encoder has 2n input lines and n output lines. In encoder the output lines generate the binary code corresponding to the input value. 7. What is priority Encoder ? A priority encoder is an encoder circuit that includes the priority function. In priority encoder,  if 2 or more inputs are equal to 1 at the same time,…
• 555555555541. A certain BCD-to-decimal decoder has active-HIGH inputs and active-LOW outputs. Which output goes LOW when the inputs are 1001? (a) 0 (b) 3 (c) 9 (d) None. All outputs are HIGH.
• Combinational Circuits » Exercise - 16. A multiplexer is a logic circuit that : (a) accepts one input and gives several outputs (b) accepts many inputs and gives many outputs (c) accepts many inputs and gives one output (d) accepts one input and gives one output