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Altera_Forum's avatar
Altera_Forum
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15 years ago

Acex 1k Open Drain outputs

On Acex 1k device do I have to specifically disable the clamping diode to use an I/O pin as an open drain output with a pull-up to 5V? Data sheet Table 13 does not indicate any requirement to do this (it only refers in Note 1 to disabling the clamping diode on inputs at a voltage above Vccio) but this seems wrong. Does anyone know whether configuring an I/O pin as an open drain output automatically disables the clamping diode?

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    My guess is it doesn't, but I wouldn't care too much about the clamping diode being automatically disabled or not. Just go ahead and disable clamping specifically. In the worst case the setting would be redundant, but it would be harmless.

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    I don't exactly understand the question, because no clamping diodes are turned on by default (also not with ACEX1K). So the obvious action is not to turn on the clamping diode for open drain outputs intended to swing above VCCIO.