AVR-Chat

Peter Gargano wrote:
> I have the reverse concern - Driving AVRs from parts designed to be 
> used with TTL. Most AVRs (eg Mega-168) have a 0.6VCC spec. on VIHmin 
> meaning 3.0 Volts when run at 5.0 Volts (well, actually worse case is 
> 0.6 x VCCmax which may give VIHmin of 3.15 Volts).
> 
> Many parts you may want to interface to an AVR have a VOHmin of 2.4 
> Volts - meaning they are not guaranteed to drive the minimum required 
> 3.0 Volts.
> 
> So, how come people can get away with it? Here's an example (and I 
> could quote many more, I use this example because it was ready to hand).
> 
>    http://www.prllc.com/productcart/pc/viewPrd.asp?idproduct=9
> 
> If you check the schematic on the User's Guide you'll see they have a 
> Samsung memory chip (with the above VOHmin of 2.4) interfaced directly 
> to the M128 running at VCC of 5.0 Volts (VIHmin of 3.0 Volts).

If you look at fig.182 of the ATmega16 data sheet, you'll find that VIHmin=1.9V,
so the 3V spec must be at some 3-5 sigma distribution point.