Interfacing TTL and CMOS logic

[Jezz Brookes]

>I need to drive a logic CMOS IC from a TTL source (actually a port of a
>8051).
>The power supply of the TTL source is +5V, while the CMOS IC is +15V.
>Of course, direct interfacing is impossible, especially because the
>'positive' level of the TTL
>output (typically 3.5V) is not sufficient for the CMOS. So I need to put
>some buffer in between.


Depending on how many line you want to drive, maybe you could use a simple
transistor switch? It would invert the signal but as it's coming directly
out of the 8051 it should be possible to invert the pin in software and have
the transistor re-invert it.

Ok, if you want to do several lines some sort of open collector buffer chip
would be the way to go in terms of PCB real estate.

Jezz.