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Altera_Forum's avatar
Altera_Forum
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20 years ago

How to read output port?

I need to read state of some output ports in my application.

In some part of the program I write these ports and in other part I want to read actual state and I wouldn't like to use special variables to keep the states.

I cannot quite understand the "tristate" meaning in Altera peripheral handbook, but it seems to me that this is what I need. I already have tested it (with first setting the direction of the port to 1 to become tristate) and it seems to be working fine. Since I don't fully understand the datasheet explanation, can somebody please confirm that I am doing it right and not setting something else, which can eventually cause some problems in my application?

Peripheral handbook says this:

<div class='quotetop'>QUOTE </div>

--- Quote Start ---

Bidirectional (tristate) ports:

In this mode, each PIO bit shares one device pin for driving and capturing data.

The direction of each pin is individually selectable. To tristate an FPGA I/O pin, set

the direction to input.[/b]

--- Quote End ---

1 Reply

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

    there are two cases for ports:

    1. port signals are connected to real in/outputs of fpga

    ( i think it&#39;s ok to use tristate signals to read back the setting of

    the outputs)

    2. port signals are used internal in fpga

    (tristate does not make sense, I don&#39;t know if quartus syntesizes

    tristate registers away ?)

    because I had some signals with case 2 and also wanted to read back

    the settings of the outputs, i made ports with input and output

    (no tristate) and connected in/outputs of these ports together

    in the top schematic.

    perhaps someone from altera can explain what will happen if i use tristate for

    internal port signals ?