[sdiy] Best way to interface 3V and 5V logic ICs on the same circuit ?

[René Schmitz]

jbv wrote:

> What is the best way to interface different logic ICs on the same
> circuit, some using 5V and others using 3V (like a uC using 3V
> and a DAC or external RAM using 5V) ?

HCT gates have TTL compatible thresholds, which you can drive with 3.3V 
logic. Interpose some HCT buffers and you're set.

The other way round can be done with 1k series resistors and a shottky 
clamp diode to Vcc. (Most CMOS inputs can handle Vcc+0.6V) However speed 
might be impaired because of the higher impedance.

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159