8-Bit Ripple Carry Multiplier using 4-Bit Adders

[tmlee2]

Hey Everyone,

I want to design an 8-bit Multiplier, using 4-bit Adders. I created a Ripple Carry Multiplier using 16 4-bit adders, but after debugging realized it doesn't work. I got this schematic off of a 4-bit multiplier i saw online, but can't find the link to it anymore.

Here is the schematic I created:

SUMMARY HOW IT WORKS:
Mantissa 1 (A7-A0) go into A7-A0 of each ADDER stage.
Mantissa 2 (B7-B0) go into the CI of each ADDER stage.
0’s go into the first stage of B7-B0, to initialize it.
The output of each stage (X7-X0) go into the input of next stage (B7-B0).
The results (P7-P0) are on the CO of each stage, and the outputs of the last stage (X7-X0) are P15-P8.

If someone could please help me correct it or see any mistakes or know of any another way to create an 8-bit multiplier using 4-bit adders. Thank you for your time and help!

 

[Mordred]

Its in the adressing take the lower 4 bits connect to the one 4 bit adder. Take the upper 4 bits to the second adder. Have the same signal activate both Chip enable pins. you will have to connect the output of a3to a1 of the second 4bit adder. This will essentially make 2 4bit adders act as one 8bit adder. a
A0to A3 connect output a3 to A0 input of second adder. On the
second adder adress as A4 to A7

edit forgot to mention each output of the adder needs to connect to the input of the next bit.
Ao output to A1 input a1 ouptut to a2 input repeat till A7

 

[tmlee2]

Thank you for your feedback, but the IC's I am using (74HC283) do not have an enable pin, so that solution won't work, I should have listed that before.

EDIT: Do you know any 4-bit adder ICs with an enable on it? That would be very helpful.

 

[Mordred]

The method I described was utilizing a flip flop circuit as an adder. The chip you described works differently. Its been sometime for me on the circuit I described I would recommend you post the datasheet for the chip you have. I am on my phone atm so would be tricky for me to do so.
However the datasheet may provide the answer you need at least it will help us with your circuit.

 

[Mordred]

http://www.circuitstoday.com/half-adder-and-full-adder

this article combined with the datasheet will probably help you. If you look at the logic diagram on your datasheet you will probably see a similar circuit built into the chip.

 

[tmlee2]

I have found a solution to my problem, I can do what you described above but need 2-input AND gates to drive each stage and still use my 4-bit Adder ICs. Thank you for your help!

 

[Mordred]

No problem glad you found the solution