Logism Circuit Design Help. HEX Display

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Joined Oct 23, 2019
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


Joined Dec 29, 2010
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



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

bin2bcd in proteus crop.PNG

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.

    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
Last edited:


Joined Mar 30, 2015
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:


Joined Apr 11, 2010
What is a HEX display? Do you mean 7 segment displays?

“1110” displayed in hex is 0E. 14 is a decimal display. A four bit value displayed in hex only requires one 7 segment display

Please clarify if your outputs are hex, bcd or decimal.