BCD multiplier

[stanley85]

Hey guys,this is a great forum instead...!
I need help and guidance to build a one bit x one bit BCD multiplier...!I have google for it and found nothing on it!For this design,i'm am not allowed to use counter and address to use only basic equipment such as mux,demux,ic and basic gates..!Any idea on how to design it?
Thanks

 

[Pommie]

1 bit * 1 bit multiply = 2 bit answer.
Take the 2 inputs to an xor gate and the output is bit 0 of the answer.
Take the 2 inputs to an and gate and the output is bit 1 of the answer.

Mike.

 

[stanley85]

1 bit * 1 bit multiply = 2 bit answer.
Take the 2 inputs to an xor gate and the output is bit 0 of the answer.
Take the 2 inputs to an and gate and the output is bit 1 of the answer.

Mike.

i still dont get it..!
my question,let say 3 (0011 BCD) * 9 (1001 BCD) the output will be 27 (0010 0111).
How do i combine full adder or other equipment to design a circuit to get the output in BCD?This is wat i meant by one bit*one bit BCD multiplier.Anyone can help me in solving this porblem..!
Thanks for your reply..!

 

[shahzad-h]

do u need multiplier circuit which multiply two four bit number and gives answer in BCD form

 

[stanley85]

do u need multiplier circuit which multiply two four bit number and gives answer in BCD form

yeah,if it is possible,i'm interested to see the circuit..DO you have it?

 

[on1aag]

4 bit multiplier.

Hi Stanley85,

If one of the two 4-bit words is "0" the result should also be "0".
If one of the 4-bit words is "1" the result should be equal to the
other 4-bit word. If one of the 4-bit words is "2" the result should
be equal to the other 4-bit word, but shifted one position to the
left. If one of the 4-bit words is "3", the result should be equal to
the other 4-bit word, but shifted one position to the left and added
to this 4-bit word. If one of the 4-bit words is "4", the result is equal
to the other 4-bit word, but shifted two positions to the left. If one
of the 4-bit words is "5" the result should be equal to the other 4-bit
word, but shifted two positions to the left and added to this 4-bit
word, and so on . . . .
The final circuit will have eight inputs and also eight outputs.
I really don't have a clue what this circuit should look like, I got my
degree by asking questions on forums like this.

on1aag.

 

[stanley85]

Hi Stanley85,

If one of the two 4-bit words is "0" the result should also be "0".
If one of the 4-bit words is "1" the result should be equal to the
other 4-bit word. If one of the 4-bit words is "2" the result should
be equal to the other 4-bit word, but shifted one position to the
left. If one of the 4-bit words is "3", the result should be equal to
the other 4-bit word, but shifted one position to the left and added
to this 4-bit word. If one of the 4-bit words is "4", the result is equal
to the other 4-bit word, but shifted two positions to the left. If one
of the 4-bit words is "5" the result should be equal to the other 4-bit
word, but shifted two positions to the left and added to this 4-bit
word, and so on . . . .
The final circuit will have eight inputs and also eight outputs.
I really don't have a clue what this circuit should look like, I got my
degree by asking questions on forums like this.

on1aag.

I appreciate your help but i 'm not sure i understand bout ur explanation...!DEfinitely the circuit will have 8 inputs but the number is constrained till 9 cause in BCD and the output must be in BCD form as well!I can say that the maximum input will be (1001)*(1001) and the rest which are more than 9 can be considered as "dont care".I just can't figure it out how the circuit going to look like...!

 

[shahzad-h]

I have the circuit but very complicated containing 80 to 85 logic gates i m not understanding how to post u

 

[stanley85]

I have the circuit but very complicated containing 80 to 85 logic gates i m not understanding how to post u

wat format the files in...!Are you using any simulator!If it is not a trouble for you,you can always e-mail me..!
my email is ahsiong_world@yahoo.com
thanks a lot!

 

[Papabravo]

There are eight inputs which represent 256 combinations. Not all of the combinations are legitimate BCD values. There are 100 valid BCD combinations. For each of those 100 combinations there are eight output values that you can compute. Each of the eight outputs is a boolean function of the eight inputs.

Your task weedhopper is to write down the eight boolean equations of 8 variables. Even after you have done this you wont really know if you are correct unles you build it or simulate it.

 

[stanley85]

There are eight inputs which represent 256 combinations. Not all of the combinations are legitimate BCD values. There are 100 valid BCD combinations. For each of those 100 combinations there are eight output values that you can compute. Each of the eight outputs is a boolean function of the eight inputs.

Your task weedhopper is to write down the eight boolean equations of 8 variables. Even after you have done this you wont really know if you are correct unles you build it or simulate it.

IS there any simple way to get the equation without using boolean..!Do you know anywhere i can get the example of the circuit...!100 combination,it will take a long time to get to it right...?

 

[Papabravo]

Sorry man that's as good as it gets.

 

[stanley85]

ok,thanks for your suggestion..! still hoping to find the example of the circuit..!thanks ya

 

[on1aag]

4-bit BCD multiplier.

Hi Stanley85,

Shifting to the left is multiplying by two, shifting to the right is
dividing by two. This can be done using multiplexers. The addition
can be done by a BCD full adder like the 74HC583.

Have much fun,

on1aag.

 

[stanley85]

Hi Stanley85,

Shifting to the left is multiplying by two, shifting to the right is
dividing by two. This can be done using multiplexers. The addition
can be done by a BCD full adder like the 74HC583.

Have much fun,

on1aag.

opps,havent learn bout that yet!That's why i need example of it so i could understand the whole process of design it...!SOrry for asking,do you know anyplace that i can search for it?

 

[philba]

sure, you can create complex combinational and/or sequential logic or you can use a 256 x 8 memory. EPROMs are pretty cheap and easy to use. your input is the two 4 bit BCD values as the address and the value at that location is the result. just fill out the 256 entry array with the values you want. The performance is basically the cost of one EPROM access.

hope your teacher appreciates the help you are getting here.

table lookup, it's A Good Thing.

 

[stanley85]

sure, you can create complex combinational and/or sequential logic or you can use a 256 x 8 memory. EPROMs are pretty cheap and easy to use. your input is the two 4 bit BCD values as the address and the value at that location is the result. just fill out the 256 entry array with the values you want. The performance is basically the cost of one EPROM access.

hope your teacher appreciates the help you are getting here.

table lookup, it's A Good Thing.

I'm not sure that i understand your advice.!HAvent learn bout it yet..!Anyway,stil appreciate ur help..!

 

[on1aag]

4-bit what was it ?

Hi Stanley85,

Try this link:

https://www.electro-tech-online.com/custompdfs/2006/10/lecture20-multipliers.pdf

on1aag.

 

[stanley85]

will try it at once!thanks a lot!