Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [adder]

Digital circuits that adds values

An adder or summer is the designation of a digital circuit that adds values.

For more details refer to this article.

268 questions
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Parallel prefix adder cells in Negabinary

I'm trying to design a parallel prefix adder for a negabinary based adder. Negabinary is base \$-2\$ instead of the familiar base \$2\$ binary. Each 1 bit adder generates a sum and two (instead of one in binary) carries that go to the next adder.…
gilianzz
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How should I understand FPGA architecture?

I've been given the task to make a 2-bit adder by programming a FPGA. The FPGA is seen below: However, I don't even know how to begin this task, because I don't understand what I am looking at. What are all those green lines supposed to do, and…
Carl
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What are carry-lookahead adders and ripple-carry adders?

I see carry-lookahead adders and ripple-carry adders terms being used often. I have no idea what either means (nor the type of architecture they describe). Can someone please explain what each one is, why one may be faster than the other, and what…
Bob John
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Designing a simple ALU

I need to design an ALU with two 8-bit inputs A and B and control inputs x, y, and z that supports the following operations: x y z | operation 0 0 0 | S = A-B 0 0 1 | S = A+B 0 1 0 | S = A*8 0 1 1 | S = A/8 1 0 0 | S = A NAND…
norman
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check if an unsigned binary number is divisible by 15

I'm a computer science student and I got stuck on this question for hours. We have a binary unsigned number X, represented by 12 bits. We would like to build a system with 1 bit output - Y, that will be '1' if X is divided by 15 without a…
sheldonzy
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Critical path for Carry-Skip adder

Can anybody explain why Carry-Skip adder has the same critical path as regular Carry-Ripple adder. My textbook says that critical path occurs when carry is generated in LSB and then propagating it through the remainder of the adder. The way I see…
Alex
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What is the minimum amount of 1bit Full Adders required to implement the equation 4X + 3Y + 13?

Using 1bit FAs and 0/1 constants only, while X(x1,x2,x3) and Y(y1,y2,y3) are 3bit each. It is possible to implement it easily with 7FA, and there's a solution with 6FA as well. Is there a solution with 5 or less? If not, why? Is there any systematic…
Dvir
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What does "2 digit BCD number" mean?

When I read it, I think a \$2\$-digit BCD number is something between \$0\$ and \$99\$ in decimal. So, for example, \$0100 1001\$ is a \$2\$-digit BCD number and decimal equivalent of it is \$49\$ in my opinion. However, this question confused me.…
muyustan
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How to determine overflow from an adder/subtractor?

I suppose in binary addition (no negative numbers), overflow happens when theres a carry out? Then for subtractor (2s complement), how do I determine it? From my understanding of my lecture notes, overflow happens when theres a change in sign or…
Jiew Meng
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Floating point addition. Are guard, round and sticky bit always necessaryl? analysis of a special case

I've a particular case of floating point addition. As you know for given floating point numbers \$x,y\$ one of the steps of the addition involves the fixed point sum: $$ s = 1.m_x + (-1)^{s_x \oplus s_y} 2^{-\delta}1.m_y, $$ I'm assuming $ |x| > |y|…
user8469759
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How to determine if a Carry Look Ahead Adder Overflows

I am implementing a 32 bit CLA Adder like how a 16 bit adder is implemented in Wikipedia Problem is how do I determine if the block overflows? I will need the carry into bit 32 (which is now in the last 4 bit CLA Adder) and XOR with carry out of…
Jiew Meng
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What is the purpose of a "carry in"?

I'm currently trying to learn how binary adders work, but I don't understand what a "carry in" is for. What is the purpose of a "carry in"?
Ethan Bierlein
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Carry Look Ahead adder propagation delay calculation

I'm studying Digital Design and Computer Architecture book, I'm stuck in the section of the carry-lookahead adder because there's something that I don't fully understand about the propagation delay of an N-bit carry-lookahead adder. The book…
Tortellini Teusday
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What is wrong with my 2-bit adder?

I attempted to build an 8-bit adder in Logisim by carefully chaining together a half-adder and 7 full adders, all made from basic logic gates. Unfortunately, it produced erroneous results; for example, 00000011 + 00000011 = 000000100 ! I found that…
norman
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Test Cases for 16-bit Ripple Carry Adder

I'm working on a lab for a course I have on VHDL, and part of it is to implement an n-bit ripple carry adder and then test it as a 16 bit adder. My problem is that I don't really know HOW to test it, or rather what inputs to give it to test it…
Matt
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