Combinational circuit for BCD to seven segment.

Hi everyone. I need some help to understand the language of a question I am doing from a textbook.

The question is :
"Design a combinational circuit for a BCD to seven-segment code converter that will input a BCD
number and output it on a seven segment common-anode display. The code converter will only
display the number 8. The converter will turn the display OFF for all other valid BCD digits except
digit 9 which will never occur. Draw a schematic using gates. Show all steps clearly."

I dont understand the part where it says "digit 9 which will never occur". Does this mean that the input 1001 will not be considered at all in the truth table, or, that it will be considered with "dont care" as output.

I realise that its a silly question and I think that the first case is correct and input 1001 should not be considered. But it would be helpful if I could confirm it with you.

It's a goofy question. I would assume, like you, that 1001 will never occur. I think this is a hint as to how to simplify the design. I won't tell you yet...

This is just a single '1000 decode driving all cathodes to gnd and open / high otherwise. Not a BCD decode at all, as the problem is stated.

I

dick_freebird said:

This is just a single '1000 decode driving all cathodes to gnd and open / high otherwise. Not a BCD decode at all, as the problem is stated.

Click to expand...

If you want to see what real BCD to 7-segment guts are, the old orange TI TTL data book is your friend.