7400 ICs are always using 5V levels despite using non-5V VCC
7400 logic levels should depend on supplied VCC as these ICs can run normally with 2-6V and logic levels (VIH, VIL, VOH, VOL) depend on the VCC which is described in data-sheets. Hence 5V should be only used as a convenience when VCC is not connected at all.
2
votes
Adam
shared this idea