# equivalent logic circuit for serial multiplier

Discussion in 'Homework Help' started by cmuraztaz, Jul 9, 2012.

1. ### cmuraztaz Thread Starter Member

Mar 14, 2009
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master any idea what is the equivalent logic circuit for serial multiplier or if you have some link please post its very helpful to me..

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Mar 14, 2009
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Mar 14, 2009
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4. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
Do you understand how this multiplier works? In other words, can you describe why and how it multiplies two 4-bit values together and where the result is stored?

The could you describe what you mean by "equivalent logic circuit"? That's actually pretty vague.

Mar 14, 2009
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6. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
Is that a diagram from an example in the text, or a diagram that you developed as you worked an example? It only matters to the degree that the point of my question wasn't whether you can provide an explanation of how it works, but whether YOU understand how it works.

So now for the real question, what do you mean by an "equivalent logic circuit"? Do you mean a schematic using gates and registers that implements this adder? If so, what work have you done thus far?

7. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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yes..you got my point..so far im using 7495 and full adder...my problem is in the 7495 pin mode,sr, and sl...

by the way im using proteus 7 professional software.

because i need logic circuit that when the output is 1 matter of millisecond
the output change to 0..I used 555 bistable but it wont stop..if I used 555 monostable we are forbidden to use push on button..that's why my last option is logic circuit...
because this output is the input of pin mode,sr, and sl...

but if you have some idea how to do this please share it ..its helpful to me..

Mar 14, 2009
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9. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
I'm having a very hard time following your description. That's an observation, not a criticism, as I can guarantee that your English is better than my ability to communicate in any other language you might speak.

Once this thing is complete, how is someone expected to interact with it?
Q1) How will then set it up (establish the multiplicand and multiplier)?
Q2) How will they start the process?
Q3) How will they know when it is done?

Once I understand that, then we can start looking at the components and the logic needed to make them do what we want.

10. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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here's the link of the circuit so far i make.
http://s1062.photobucket.com/albums/t487/cmuraztaz/?action=view&current=tweing.jpg

1. the input in 4 bit adder is the multiplicand..and the input in B7495 is the multiplier.

2. to start the the process..the Q3 in B7495 is the one who start the process...the 4 bit adder is depend only in the output of Q3 in the B7495..if the Q3 in B7495 is 1, the 4 BIT ADDER execute, because the output of Q0-Q3 is 0 in A7495, the 4 BIT ADDER add the multiplicand and the output in A7495..
just like this 1101+0000=1101..and then the mode will execute next the sr,the function of sr is what is in the input the same in the output...and then sl, the sl is the one who responsible of shifting the 4 digit..because the input of A7495 is 1101 so the output is 1101...from 1101 when it shift become 0110 and in the B7495 from 1011 when it shift 1101..by the way the S1 in 7495 is the input from the carry carry..if you look go back in #5 i post the link from "0 1101 1011" when it shift "0 0110 1101"..
when in the B7495 the Q3 is 0...no adding happen just shifting...

3.how will they know when it is done?...about this one, i don't know how to do it..but i have an idea but i don't know if its work..base on the circuit i will add some registry that when it comes 4 time shifting the process will stop..

that's all i can give the info..if you have some suggestion,correction and addition..i would appreciate...

thanks again..

11. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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but if you have any great design than this..if you can show me i would appreciate..
thanks again..

12. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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if you have better design than i made...and if you can show me i would appreciate..

13. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
I think you've misunderstood my first two questions, but it appears that the third question has you beginning to think of some of the issues.

So let me rephase my questions a bit more clearly.

Situation: You have built the circuit and go to Bob to have him test it. You set it on the table in front of him. Bob wants to multiply 13 (1101) by 9 (1001). The questions are meant to be interpretted in the vein of what you would tell Bob, who has never seen this thing before, when he asks, "How do I use this to multiply 13 by 9?"

1) How does Bob get the values 13 and 9 into your circuit? Are there two sets of DIP switches that he sets? Does he press any kind of LOAD button?

2) Once Bob has gotten the values into the circuit, how does he make the circuit start the compution?

3) Once the computation is complete, how will Bob know that?

Hopefully, some of this has been specified for you. You talked about certain things being forbidden, that (hopefully) means that what is allowed and/or required has been made clear, as well.

14. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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i think the one i post its doesn't work..here's the link you can view what im talking about.
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1. yes there's a button to press
2. i think its auto compute because my software I used, I just press the play and then u can compute the value and every component I use there's no power supply connected..
3. to stop the loop..i have no idea how to do this..

but if you have some idea or design..i would appreciate..

15. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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if you see there's eight zero's ..that's the output..

16. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
Is this something that you are expected to actually build and demonstrate (which I have been assuming since you were talking about using a 7495). What are you using for the full adder?

Since you have a button that the user presses to load the values, you can use that same button to start the thing running. There are a number of ways to do the necessary cycle counting in order to know when to stop. Perhaps the simplest is to use another 7495 to shift a bit from one end to the other and look for that bit to make it to the end of the shift register in order to signal that it is time to stop.

So write a detailed event pipeline (which is very analogous to pseudocode). This is nothing more than a step-by-step of the actions you need performed with respect to each element of the design. For example (and this is a junk pipeline that I'm making up from thin air):

WHILE (BTN is LO)
Do Nothing (waiting for person to press button)
WHILE (BTN is HI)
Do Nothing (waiting for person to release button)
LOAD multiplier into shift register Q and clear shift registers A and T
WHILE (lsb of T is LO)
IF (lsb of Q is HI)
SHIFT Q to the right
SHIFT A to the right
SHIFT T to the right

Once you have a detailed event pipeline that we think will work, then we can figure out how to make each of those things actually happen with the parts you have access to.

17. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
This makes no sense. If the output is when I see that there's eight zero's and that's the output, then what purpose does the circuit serve? The output is simply eight zeros.

18. ### cmuraztaz Thread Starter Member

Mar 14, 2009
13
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i mean there's the output display...sorry about that..

what ever the output of A7495 will be add in the 4 BIT ADDER

thanks for you quick feedback..I'm doing right now what you told...
thanks you..

i post later what is the outcome

19. ### WBahn Moderator

Mar 31, 2012
23,070
6,924
Something will always be displayed. How will the person know that what they are seeing is the final result?

You still haven't said what you are using for the 4 bit adder. If I had asked, "What are you using for your shift registers?" You would have said, a 7495. So, what are you using for your 4 bit adder?

20. ### absf Senior Member

Dec 29, 2010
1,853
505
I think the OP is using the 74LS283 for the adder. But I dont know what is the single bit thing that labelled as "ADD". Is there such a gate in existence?

I think the whole schematic is missing the clock control. How does the multiplier step through the four sequences without clock pulses?

Allen