[aprssig] GPS GT-320FW(AS)

Jason KG4WSV kg4wsv at gmail.com
Sun Apr 21 20:50:03 CDT 2013


On Sun, Apr 21, 2013 at 7:32 PM, Glenn Little WB4UIV
<glennmaillist at bellsouth.net> wrote:
> If the level is TTL, by definition, it is 2.2-5.0V for high and 0-0.8V for
> low.

That may be, but many 5V devices have a higher voltage requirement for
high.  The ATmega8, for example, requires 0.6*Vcc, which is 3V when
Vcc = 5V.

Combine this with the fact that the minimum output high voltage for
3.3V devices is not necessarily 3.3V - for example, a 3.3V device I've
been working with has a minimum of 0.8*Vcc, so at 3.3V you're only
guaranteed 2.64V - a problem if you want to talk to the aforementioned
5V ATmega8 when it needs 3V.

-Jason
kg4wsv


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