Can this circuit validate AT89Cx051 micro if best valued components are used?
Arranging diodes that way doesn't give you a NOR gate. There is no way to create a NOR gate using only diodes, as diodes cannot invert a signal.

Diode logic can only be used to create AND or OR, and even then you need a pull-up/down resistor:







simulate this circuit &ndash; Schematic created using CircuitLab