Tristate Buffer Output if Input is High-Z?

Chuck Guzis cclist at
Tue Sep 27 11:49:44 CDT 2005

On 9/26/2005 at 6:09 PM Jeff Walther wrote:

>If a tristate buffer is enabled by its control line, but the input to 
>the buffer is at high-Z is there a typical output?

I think I understand what you're asking, but I'm not sure.

If it's straight bipolar TTL, the high-Z input is usually at a "high" level.  But iwith CMOS, you're in terra incognita.  Stray charges can linger on lines a lot longer than on bipolar.  Better to add some pullups--it shouldn't take much to clamp the inputs at a "high" state--100K should be fine.  10K will work fine on LSTTL.


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