2. Short questions Let us consider a 4-bit binary counter that counts from 0 to

Question

2. Short questions Let us consider a 4-bit binary counter that counts from 0 to 15 and then resets to 0 and starts up again. Do you need additional logic to go from 15 to 0 such as checking if the output of the counter is 15? Why? a. b. Let us consider a 4-bit shift register that only supports shift right operations. How many D flip-flops do we need to implement this shift register? If this register was modified to become a bi-directional shift register, how many D flip-flops would it take then to implement the new shift register? Combinational logic functions are sometimes implemented using look-up tables (like in Altera FPGAs). The look-up table contains results for all possible combinations of the input. If the maximum number of inputs per look-up table was 5, how many look-up tables would it take to implement a 7-variable function? c.

Explanation / Answer

A. No additional logical circuit is required to make transition from 15 to 0 as the shift register is designed in such a way that when output of each flipflop become high that is 1111 the next state is 0000. Therefore output goes from 15 to 0 automatically. In order to manipulate counter that is to make the counter to count any other sequence than 0,-15 or 15-0 we will require additional logic circuit.

B. The number of D flipflops required is equal to the number of bits of shift register in both uni directional and bidirectional shift registers.The two types just differ in the way through which these flipflops are connected. Therefore number of D flipflops required in each case is 4.

Please post the last part seperately. Sorry for the trouble

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