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Altera_Forum
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15 years ago

Detect Tristate 'Z' signal?!

Hello, I have a state machine (VHDL) that should switch on an external input signal. My problem is that the input signal maybe not driven by any device, so it's value is 'Z'. How can I avoid tha...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

I am not sure about Z simulation issue.

remember Z on your input is not a logic value but a case of high impedance which can go to logic 1 or zero by just touching... if input is not connected (not driven) then you can either think of it as unknown logic or being driven through air (high impedance).

In similation: you define your inputs as 1 or 0 but you may try Z vector and see.

Note:

I have used weak pullup before in similar problem with state machine in Max II and it worked.