Logic threshold level chart

There are quite a lot of digital logic families that differ in their I/O voltage levels. Mainly we use 5V and 3.3V levels in our projects. And there is always dilemma to communicate 5V with 3.3V devices. In many cases a 3.3V devices come with 5V tolerant pins but it is better to know than guess.

Here is a nice concentrated chart that provides visual information on how these logic level thresholds differ among technologies. Chart include CMOS, TTL, mixed TTL/CMOS, ETL, BTL, GT, low voltage glue logic families. FYI most CMOS families are tolerant to 5V input and probably you won't, need a logic level converter in many cases. This is OK in hobby level, but if you are designing end product to market then it is better to place a level converter to ensure reliable operation.