Tristate Buffer Output if Input is High-Z?

[Tony Duell]

> 
> 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?

No, the input will float. _Most_ TTL buffers have inputs that should 
float high (so the output will be whatever you should get for a high 
input), CMOS ones will pick up random noise. A very few buffers will 
float low, I think.

If you require the output to be at a known state under such condtions, 
you need to ensure the input is at a known state too, e.g. by adding a 
pull-up resistor.

One thing you can be sure of is that the output will not be 
high-impedance if the buffer is enabled. The bit of your message that I 
deleted seems to suggest you were hoping it would be. 

-tony