Classle

Frequently Asked Questions - Digital Electronics

IC's has many gates integrated within them. Wat does the gates(AND,OR,NOT ...) consist of?

Answer1

NOT gate (inverter)

The output Q is true when the input A is NOT true, the output is the inverse of the input: Q = NOT A
A NOT gate can only have one input. A NOT gate is also called an inverter.

traditional NOT 
gate symbol IEC NOT gate 
symbol
Input A Output Q
0 1
1 0
Traditional symbol IEC symbol Truth Table

 

AND gate

The output Q is true if input A AND input B are both true: Q = A AND B
An AND gate can have two or more inputs, its output is true if all inputs are true.

traditional AND 
gate symbol IEC AND gate 
symbol
Input A Input B Output Q
0 0 0
0 1 0
1 0 0
1 1 1
Traditional symbol IEC symbol Truth Table

OR gate

The output Q is true if input A OR input B is true (or both of them are true): Q = A OR B
An OR gate can have two or more inputs, its output is true if at least one input is true.

traditional OR 
gate symbol IEC OR gate 
symbol
Input A Input B Output Q
0 0 0
0 1 1
1 0 1
1 1 1
Traditional symbol IEC symbol Truth Table

Answered by: classlerishi     On: 26-Aug-2011


Dear Guest,
Spend a minute to Register in a few simple steps, for complete access to the Social Learning Platform with Community Learning Features and Learning Resources.
If you are part of the Learning Community already, Login now!

want to learn disital system design but how and where i found rich amount of content writtten on digital system design a

Answer1

You can refer  Digital Systems and Design by Morris  Mano. It provides the best on learning the fundamentals. Hope they provide a CD along with the book and you can refer to it.

Classle has a collection of NPTEL Lectures on Digital Systems and Design.Please refer www.classle.net/category/tags/electronics-digital-systems-design


Answered by: kbkarthick     On: 20-Jul-2011

Answer2

You can refer  Digital Systems and Design by Morris  Mano. It provides the best on learning the fundamentals. Hope they provide a CD along with the book and you can refer to it.

Classle has a collection of NPTEL Lectures on Digital Systems and Design.Please refer www.classle.net/category/tags/electronics-digital-systems-design


Answered by: classlerishi     On: 26-Aug-2011


Dear Guest,
Spend a minute to Register in a few simple steps, for complete access to the Social Learning Platform with Community Learning Features and Learning Resources.
If you are part of the Learning Community already, Login now!

Which one is superior: Asynchronous Reset or Synchronous Reset

Answer1

Why Reset?

A Reset is required to initialize a hardware design for system operation and to force an ASIC into a known state for simulation.

A reset simply changes the state of the device/design/ASIC to a user/designer defined state. There are two types of reset, what are they? As you can guess them, they are Synchronous reset and Asynchronous reset.

Synchronous Reset

A synchronous reset signal will only affect or reset the state of the flip-flop on the active edge of the clock. The reset signal is applied as is any other input to the state machine.

Advantages:

  • The advantage to this type of topology is that the reset presented to all functional flip-flops is fully synchronous to the clock and will always meet the reset recovery time.
  • Synchronous reset logic will synthesize to smaller flip-flops, particularly if the reset is gated with the logic generating the d-input. But in such a case, the combinational logic gate count grows, so the overall gate count savings may not be that significant.
  • Synchronous resets provide some filtering for the reset signal such that it is not effected by glitches, unless they occur right at the clock edge. A synchronous reset is recommended for some types of designs where the reset is generated by a set of internal conditions. As the clock will filter the logic equation glitches between clock edges.

Disadvantages:

  • The problem in this topology is with reset assertion. If the reset signal is not long enough to be captured at active clock edge (or the clock may be slow to capture the reset signal), it will result in failure of assertion. In such case the design needs a pulse stretcher to guarantee that a reset pulse is wide enough to be present during the active clock edge.
  • Another problem with synchronous resets is that the logic synthesis cannot easily distinguish the reset signal from any other data signal. So proper care has to be taken with logic synthesis, else the reset signal may take the fastest path to the flip-flop input there by making worst case timing hard to meet.
  • In some power saving designs the clocked is gated. In such designed only asynchronous reset will work.
  • Faster designs that are demanding low data path timing, can not afford to have extra gates and additional net delays in the data path due to logic inserted to handle synchronous resets.

Asynchronous Reset

An asynchronous reset will affect or reset the state of the flip-flop asynchronously i.e. no matter what the clock signal is. This is considered as high priority signal and system reset happens as soon as the reset assertion is detected.

Advantages:

  • High speeds can be achieved, as the data path is independent of reset signal.
  • Another advantage favoring asynchronous resets is that the circuit can be reset with or without a clock present.
  • As in synchronous reset, no work around is required for logic synthesis.

Disadvantages:

  • The problem with this type of reset occurs at logic de-assertion rather than at assertion like in synchronous circuits. If the asynchronous reset is released (reset release or reset removal) at or near the active clock edge of a flip-flop, the output of the flip-flop could go metastable.
  • Spurious resets can happen due to reset signal glitches.

Conclusion

Both types of resets have positives and negatives and none of them assure fail-proof design. So there is something called "Asynchronous assertion and Synchronous de-assertion" reset which can be used for best results.


Answered by: siva85     On: 29-Apr-2011


Dear Guest,
Spend a minute to Register in a few simple steps, for complete access to the Social Learning Platform with Community Learning Features and Learning Resources.
If you are part of the Learning Community already, Login now!

how do i design 2 bit magnitude comparator by logic gates?

Answer1

can try with mux to reduce complexity


Answered by: pradeepkumarp     On: 25-Apr-2011


Dear Guest,
Spend a minute to Register in a few simple steps, for complete access to the Social Learning Platform with Community Learning Features and Learning Resources.
If you are part of the Learning Community already, Login now!

how computer languages are installed in electronic devices?

Answer1
By copynig the program which is compiled into the byte code of the processor present in the elecronic device.  There would be additional circuitary arrangemetn and programs already in the device for bootstrap which subsequently will read the new program and execute them when required.

Answered by: Vaidya     On: 28-Mar-2011


Dear Guest,
Spend a minute to Register in a few simple steps, for complete access to the Social Learning Platform with Community Learning Features and Learning Resources.
If you are part of the Learning Community already, Login now!