# tri-state buffer

Discussion in 'Homework Help' started by zulfi100, Feb 22, 2013.

1. ### zulfi100 Thread Starter Member

Jun 7, 2012
320
0
Hi,
Can some body plz guide me with the following question:

I know about the G input and V0 output but i dont know about the control line. If G is High, V0 is either 0 or 1. In this situation we cant say its behaviour is similar to which gate? If G is Low, V0 is open.

Zulfi.

2. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Tri-state buffers are available with either active high or active low enable (control). Which one are you talking about?

3. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
Make a truth table for your input and output under the condition that the control signal is HI. That matches the truth table for what gate?

4. ### zulfi100 Thread Starter Member

Jun 7, 2012
320
0
Vi G V0
L L Open
H L Open
L H L
H H H

If Vi is the input then its same like output. Its a buffer. So its not similar to any gate (Correct?). What is G here?

Zulfi.

5. ### ScottWang Moderator

Aug 23, 2012
4,933
777
You can check 74LS126, it matched what you need.

You can also see the 74LS125, the ctrl pin is opposite of 74LS126.

6. ### zulfi100 Thread Starter Member

Jun 7, 2012
320
0
Sorry, i cant access this page. I have even tried google but i cant connect with datasheet page.

Zulfi.

7. ### ScottWang Moderator

Aug 23, 2012
4,933
777
I tried on google chrome and IE8, they are ok.

You can seacrh on google as 74LS126, then you will get a lot of infos.

8. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
Since they are specifying that G is HI, the truth table is reduced to just those rows in which G is HI. Then, because all of the surviving rows have G in the same state, the entire column can be removed and just a note placed near the table indicating that it is for the case when G is HI.

You are correct that the result is the same as a buffer, but a buffer is a logic gate just like an inverter is. It's just not a very interesting one from a logic standpoint -- but it is often a very important one from the standpoint of getting a design on paper to work in the real world.

9. ### zulfi100 Thread Starter Member

Jun 7, 2012
320
0
Hi,
Thanks for all of you for helping me.
I have IE9. Its closing.

Book (Digital principles and application, 5th edition, page=11) says its the buffer but the answer (which is another book) says that its a 'NOT gate".

However on the same page book says that TRI-state inverter is a NOT circuit.

This means both TRI-STATE- Buffer and TRI-STATE-Inverter are not gates (confusing?) . Is it correct?

Zulfi.

10. ### ScottWang Moderator

Aug 23, 2012
4,933
777
TRI-STATE-Buffer -- It is a Buffer, but not an Inverter.
TRI-STATE-Inverter -- It is a Buffer, and it is also a Not Gate.

You can play the logic gates at here .

And you can see the internal structure at here.

11. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
When enabled, a tri-state buffer is a buffer.

When enabled, a tri-state inverter is an inverter.

The names were not picked at random.