Perhaps he was referring to the entire method (voltage divider for
5v->3v AND just sending 3v into the 5v logic and assuming that it will
be above the logic threshold).

Sean


On Tue, Sep 29, 2009 at 11:59 AM, Olin Lathrop
<olin_piclist@embedinc.com> wrote:
> Brendan Gillatt wrote:
>> Many people will tell you that you can use a voltage divider for 5v ->
>> 3v and rely on the 5v logic's 2.5v threshold for 3v -> 5v conversion.
>> This may work but it is not bidirectional and sounds a bit iffy.
>
> I don't see anything iffy? =A0All specs are met without waving of dead fi=
sh.
>
> There is a tradeoff between speed and current consumption with the resist=
or
> divider, but that is no different than the tradeoff of what family gate to
> use for the other direction. =A0My standard answer is 2K ohms in series
> followed by 3.9K ohms to ground for 5.0V to 3.3V, but some cases may requ=
ire
> lower values. =A02Kohms // 3.9Kohms =3D 1.3Kohms, * 100pF =3D 130nS, so t=
hat
> should be good for up to 2MHz square wave considering 100pF is very high =
for
> on-board traces.
>
> Do you have any fact-based objection or is your comment just silly
> superstition?
>
>
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