# Bcd decoder problem

1. Aug 10, 2008

### zeroground

1. if i i have two "4 bit full adders" and two decoders and three seven segments and i wanted to add numbers in binary with the input and convert it to decimal and show it on the seven segments

2. i did everything and i put the "Carry out" from the first adder into the "Carry in" of the second adder But there's a problem facing me the pins "S0,S1,S2,S3" and "S4,S5,S6,S7" from the full adders how can i arrange them to show the number on the right way

this is urgent ...
thnx

2. Aug 10, 2008

### zeroground

i mean how can i put them in the two BCDs ?
How can i put the tenth alone and the hunder's alone ?

3. Aug 11, 2008

### zyh

Two "4 bit full adders" can generate a counter from 0-16, how can you generate 0 - 255?
btw, I don't like "urgent" question.

4. Aug 11, 2008

### zeroground

one 4 bit full adder has "S0,S1,S2,S3" which can be 1111 which is 15
two 4 bit full adders has "S0,S1,S2,S3,S4,S5,S6,S7" WHICH can be 11111111 wich is 255

5. Aug 11, 2008

### zyh

OK, I understand what's you mean.

I think it's impossible to get '255' from 1111 1111, because a BCD-to-7-segments can only convert the 0000-1001 to 0-9. You can't get any carry if the counter overflow by 10 or 100.

If you have three "4bit-BCD-dec-counter", your problem can be solved.

6. Aug 11, 2008

### zeroground

But 11110000 + 00001111 can get 11111111 :)

7. Aug 11, 2008

### zeroground

can u tell me what to do ?

8. Sep 18, 2008

### zyh

Hey, Have you ever finish your Task? If not, follow my suggestion I said early, what you need is three "4bit-BCD-dec-counter", Good luck.