AVR-Chat

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).

Peter


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