I have seen several products in production that use a 5V AVR with 3v ethernet chips. Although these devices are 5V tolerant, I'm concerned about reading data . Typically these 5v tolerant devices have a TTL level output, that is 2.4V min for a logic high (attainable from a 3.3V supply). However the data I/O of an avr running at 5V is not TTL level but CMOS levels. which requires a min voltage of 0.7 x VCC (3.5V) for a logic high. This would suggest a need for level translators. However these products use a design that connect directly between a 5v avr & 3.3v logic.
Am I being overly conserned about this, it obviously works, but how about over a range of temperature/voltage And doesn't CMOS devices consume more power when a signal is in the mid range.
Anybody have any thoughts on this?