# Logism Circuit Design Help. HEX Display

#### AlexVR

Joined Oct 23, 2019
1
I need to design a circuit to calculate the product of two 4-bit binary numbers, and then display the decimal result in three HEX displays.I already have the multiplication part, but the hex baffles me since :

1. 1-The inputs are two 4-bit binary numbers.
2. 2-The system can display each input binary number using two HEX displays.
• For example, if an input is “1110”, you shall display 1 4 in two HEX displays.
3. 3-The system can display the decimal result in three HEX displays.
• For example, if the result is “0110 0001”, you shall display 0 9 7 in three HEX displays.
4-To display decimal digits, the “double dabble” algorithm shall be used.

And my contrains are as follows:
1. 1-An “Add-3” circuit for double dabble algorithm
2. 2-A binary-to-BCD subcircuit with 4 inputs and 8 outputs
1. 4 inputs represent a 4-bit binary number
2. 8 outputs represent 2 BCD codes for two decimal digits, which can be used to control 2 HEX displays.
3. 3-A binary-to-BCD subcircuit with 8 inputs and 12 outputs
1. 8 inputs represent an 8-bit binary number
2. 12 outputs represent 3 BCD codes for three decimal digits, which can be used to control 3 HEX displays.

I have attached my current curcuit

#### absf

Joined Dec 29, 2010
1,947
The easiest way to do an 4 bit binary to 5 bit BCD is to program a ROM with 4 bit input and 5 (or 8) bit output. The logisim is capable of doing it if you read the tutorial. See video attached.

The other way is to find a 74185 chip to see if it is available in logisim. See datasheet attached.

Logisim using ROM

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#### absf

Joined Dec 29, 2010
1,947
This is a circuit displaying BCD 12 on an input of 1100 using proteus....

The smallest ROM I have in proteus is 2732 4kx8 eprom. So I have to tie all the unused pins to logic '0'

The code is done using a 8051 assembler.

Code:
    ORG     0000
DB    00H,01H,02H,03H,04H,05H,06H,07H,08H,09H    ;000
DB    10H,11H,12H,13H,14H,15H,16H,17H,18H,19H    ;010
end

Last edited:

#### dl324

Joined Mar 30, 2015
11,258
Welcome to AAC!
I have attached my current curcuit
Post your .circ file. You'll have to change the extension to .txt or .asc.

It would be easier to check your circuit if you didn't bus the signals.

#### dl324

Joined Mar 30, 2015
11,258
I have attached my current curcuit
I took a closer look at your schematic and all you have are adders and multiplexers. You haven't made any attempt to implement binary to BCD conversion using the double dabble algorithm.

I learned enough about Logisim to do the converter: