Hardware Questions

Q:

Give two ways of converting a two input NAND gate to an inverter.

Answer

One way is shorting the two inputs of the NAND gate and passing the input.


truth table:


A B output


1 1 0


0 0 1


The second way is passing the input to only one input (say A) of the NAND gate. Since the other input  (say B is floating, it is always logic one.


Truth table:


A B output


1 1 0 


0 1 1

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Q:

Can 8259 he interfaced with 8085 via the trap pin?

Answer

Yes... so if 8529 gives interrupt then it will be serviced immediately but since INTA pin is left hanging the INSR bit will never be set.. and so whenever my interrupt occurs depending upon priority it will be serviced.. also the ISR address for all interrupts will be same ie 0024H..


Interrupt via trap is nonmaskable, so it will be serviced immediately.

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0 2952
Q:

What is the strength of the signal transmitted by powerful cell phones?

Answer

the powerful cell phones can transmit a signal of 3 watts.

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0 2849
Q:

What are the static and dynamic hazards in logic circuits?

Answer

If for a short period of time circuits goes to some different logic level then it is spposed to have then it is called static hazard. e.g., If the final logic value of output of given circuit becomes one vent if if is supposed to be zero then it is called static-0 Hazard and vice versa. Dynamic Hazard is the one in which the circuit output goes to some other logic level more than once then finally settling down to some appropriate level.

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0 2830
Q:

How do you detect if two 8-bit signals are same?

Answer

Pass input to XOR and give their outputs to OR gate, if your output is 0 both 8-bit signals are same.


OR


Pass input to XNOR and give their outputs to AND gate, if your output is 1 both 8-bit signals are same. 

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1 2766
Q:

Suppose you have a computional circuit between two registers driven by a clock. What will you do if the delay of the combinational circuit is greater than your clock signal?

Answer

Use the concept of register-retiming.


divide the totla combinatorial delay in two segments such that individually the delay is less the clock period.


this can be done by inserting a flip-flop in the combinational path.


e.g.,


clock period --- 5 ns


total cominational delay ---- 7


then divide the 7ns path in two path of 4 or 3 (best resutls are obtained if delays are  same for both path i.e 3.5ns) by inserting a flip-flop in between.

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0 2764
Q:

Have you studied buses? What types?

Answer

There are three types of buses.


Address bus: This is used to carry the Address to the memory to fetch either Instruction or Data.


Data bus: This is used to carry the Data from the memory.


Control bus: This is used to carry the Control signals like RD/WR, Select etc.

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0 2686
Q:

Which interrupts has the highest priority?

Answer

TRAP has the highest priority


there are 2 types of interrupts external and internal. NMI has highest priority among all external interrupts, TRAP has highest priority among all internal interrupts. 

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0 2639