The PROM has 1 extra input pin and 1 extra output pin.  There is one clever way to use it !

• Extra Input Pin : BLANK if input number is 0
• Extra Output Pin : active if input number is 0

This way, the decoders can be chained and leading 0s can be blank'ed.

A simple switch tied to the MSB will select if leading 0s are blank'ed. Just like #DYPLED !