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Altera_Forum's avatar
Altera_Forum
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15 years ago

Bidirectional vs Output

Hello everybody,

I want to be able to switch an output between the usual

VDD/VSS outout, ie digital 1 and digital 0 as well as being able

to set the output to tristate, speak the pin on the other side of

my CPLD will see a high resistance input.

Is the solution to control a regular output with a tristate buffer or to

use a bidir pin with a tristate buffer in order that the externally connected

component can "see" the high impedance of the bidir pin when the tristate is enabled on the other side ?

Seems like if I use a regular output the pin on the other side will only see a 1 or a 0 on the other side.

Thanks in advance -

Eric

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    Kaz is right. You need the bidir pin only if you want to read the level possibly driven by the other side when your output is in high impedance state.

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    15 years ago

    For an output you can apply '0' or '1' or 'Z' without the need to declare bidirectional pin (normally).