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Richard Erlacher
11/07/11 07:21
Read: 356 times
Denver, Co

#184574 - let's get down to low-level details
Responding to: Arif Deshmukh's previous message
Arif Deshmukh said:
Thanks for replies.

I want to drive four Common Anode 7-segment display.
I tested on 74LS245, its out is at logic "1" when its input is kept floating or not connected to "1" or "0", so all the segment of display always on.
So I am looking for such buffer IC whose output strictly follows the input. I mean when input is 1 or 0 then only output is 1 or 0 and if input is floating output should be at high impedance.

Suggest me any other solution of this problem if possible.


Are you saying you require a buffer that not only drives the input logic level to either 1 or 0, but also senses that the input has gone to a high-impedance state? How, exactly, would you define that high-impedance state, and how would you propose to sense it?

There are buffers that offer a high-impedance output when an output enable pin is driven either high or low, depending on its type, but I know of none that straightforwardly detects a high-impedance state at its logic input. Generally speaking, you must know when you want the output to go to a high-impedance state. If you can provide an output enable, then you can use something like the 74HC125 or 74HC126. Take a look at those two datasheets and then decide whether that is what you want, and make your decision known. That will provide a starting point.

If you want to detect a high-impedance state, you have to define how you would detect it. That may not be so easy.


List of 14 messages in thread
Non Inverting Buffer      Arif Deshmukh      11/05/11 21:32      
   3 states?      Andy Neil      11/06/11 00:53      
   are You sure?      Stefan KAnev      11/06/11 03:18      
      Describe the goal - not the step      Andy Neil      11/06/11 06:46      
         bidirectional driver      Jan Waclawek      11/06/11 06:56      
   Redesign your circuit!      Kai Klaas      11/06/11 06:04      
   You've described..        Oliver Sedlacek      11/07/11 04:54      
      Goal      Arif Deshmukh      11/07/11 06:07      
         "its input is kept floating" do you mean      Erik Malund      11/07/11 06:39      
         let's get down to low-level details      Richard Erlacher      11/07/11 07:21      
         Common Anode 7-segment display      Stefan KAnev      11/07/11 08:34      
            No need to float the signals      Per Westermark      11/07/11 08:56      
         Do not let inputs float...        Michael Karas      11/07/11 09:52      
      Absolutely Right.      Michael Karas      11/07/11 10:10      

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