Questions tagged [adder]

Digital circuits that adds values

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57 views

I want to implement an Adder for 8-bit signed numbers coded with 1’s Complement representation

I am having a hard time trying to implement an adder for 8-bits signed numbers with 1's complement but without using VHDL since I am new to this kind of stuff. But I know that I should use 8 full ...
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26 views

Worst case scenerio in carry skip adder?

I am having trouble understanding this. worst case operation time takes place when carry is generated in the first block carry skips intermediate stages carry is killed in the last ...
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1answer
29 views

Design input of the 4 bit adder

I have the answer. But i'm not sure how the input of the adder is derived. Why is it a,b,1,1 for x and 0,a,b,0 for y? Been searching multiple sources but i'm stuck. Trying to study for my exams.
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53 views

Please help! Implement 4-bit Incrementer with two 74LS163 + 74LS74A + XNOR gate(s) + AND gate(s)

The Question Use two 74LS163, one 74LS74A, XNOR gates and AND gate(s) to build a circit that can "add" two given "4-bit binary numbers" A and B. Here is how the circuit computes SUM = A+B (for SUM &...
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62 views

VHDL - signed vs unsigned adder

I have made a four bit adder with carry-in & -out that contains an unsigned and signed architecture: ...
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36 views

What would happen if a negative voltage is given to an op amp adder circuit?

Would it subtract that voltage because it would reduce the total current going on the feedback resistor ?
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2answers
55 views

What is a Carry Propagate Adder?

It's in my syllabus but there's no mention of it in my book. Can someone explain to me what is a Carry Propagate Adder?
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1answer
56 views

Making a simple 4 bit adder into a 4 bit adder with carry in & out

I have coded a simple signed 4 bit adder. It doesn't have any carry in or carry out so it easily overflows. Below you can see my code. ...
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3answers
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How should I understand FPGA architecture? [closed]

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. ...
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2answers
110 views

VHDL: difference between using “+” or writing our own adder

I would like to know what would be the difference between between using "+" or writing an adder for adding two numbers: ...
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1answer
55 views

Different types of full adders

I programmed a full adder in VHDL as shown in the picture below: However, when compiling it, I get the following diagram when I open the Technology Map Viewer: My compilation report also says that I ...
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28 views

How to cascade multiple look ahead adders

I know how we can prepare 4 bit look-ahead carry adder (CLAs) to avoid delay involved in rippling of carries in ripple carry adder. We calculate various signal in CLA as follows: Carry propagate ...
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50 views

Designing a Carry lookahead unit using EEPROMs, creates osclillator

I have read something about CLUs (Carry lookahead units) and want to build one. I have settled on design using eeproms as adders ...
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2answers
58 views

How does carry in work in full adders?

Yesterday I asked a similar question and realized I still don't quite get it, so I'm sorry about that. Here is explicitly what I mean: This is a part of a full adder. The first row in which ...
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4answers
112 views

binary addition / truth table?

I'm trying to understand how binary addition works. If I understand it correctly, with two variables e.g. x and y you add a ...
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1answer
89 views

Efficiently calculate \$-x-y\$ using a single adder

I would like to know if there is an efficient way of implementing the operation \$-x-y\$ on an FPGA using only a single chain of adders or subtractors, roughly equal in length to the maximum number of ...
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3answers
113 views

How does a “standard” ripple carry adder behave?

I came across the following problem: A half adder is implemented with XOR and AND gates. A full adder is implemented with two half adders and one OR gate. The propagation delay of an XOR gate is ...
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1answer
34 views

Relative difficulty between leading zero counting and addition

Consider a 32-bit or 64-bit ALU that must implement both count leading zeros and integer addition, with low latency (say a few cycles), implemented on a modern high frequency logic process. Which is ...
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1answer
127 views

2's Complement 4 Bit adder. (Multisim)

I am hoping I am doing something dumb here. I know there are other posts about this but everything I have found leads me to believe my circuit should be working. Yes this is for homework. No, I am not ...
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26 views

ripple-borrow binary subtraction circuit

How does this patented ripple-borrow binary subtraction circuit eliminate the need for doing two-complement conversion on the input, thus saves on hardware circuit computation area and time ?
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2answers
88 views

simple six-position voting machine into a 7 position voting machine

I'm new to learning about full and half adders and what not. but I am struggling to understand this question out of my study manual. The pictures shows a simple six-position voting machine module ...
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1answer
43 views

What is the purpose of carry-in in full adder? If carry in equals carry out of previous adder, then I have question

In 5th row carry out is 0 then why is carry-in equal to 1 in next adder?
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27 views

Propagation delay in full adder models

From my last question Propgation delay I tried to solve for the time delay that occurs at the last carry Not sure if I have done it right .. Please correct me if I m wrong
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83 views

VHDL - How to add several numbers parallel

i would like to add several (variable number N, fixed size) numbers in VHDL. In the image below you see how i want to do the additions. In this example there are N=6 numbers (A0 - A5). I have a ...
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1answer
117 views

FPGA too slow for my ripple carry adder?

I wanted to make simple LED counter on my FPGA board (Cyclone IV EP4CE). I've made (from scratch - from NANDs) 4bit counter and 26 bit one. I have 26bit signal that is wired (port map) into 26 bit ...
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1answer
105 views

Full Adder driven by clock [FPGA/VHDL]

I've got Ripple Carry adder (26bit) made from scratch. ...
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1answer
72 views

3 bit full adder designing

I am new to the concepts of using adders to add numbers but I tried using the definitions which I understood as given two binary digits A, B the full adder takes three inputs A, B, C where C acts as a ...
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2answers
82 views

Full Adder Circuit

This circuit is based around the SN74HC283 4 bit full adder. What purpose does the resistor network serve? Will this circuit work without any resistors, i.e. using raw inputs and outputs? ...
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53 views

Instantiating modules in SystemVerilog

This is a picture of a system that I am building: (original) I am writing SystemVerilog for the Counter4to3 module, whilst the other modules (Full adder and half adder) have already been provided to ...
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1answer
690 views

Implementing a 4-bit ripple carry adder/subtractor using structural VHDL

I have to create a 4-bit ripple carry adder/subtractor. The circuit will have two 4-bit data inputs (A and B), a control line (Add/Sub), a 4-bit data outputs (S) and a carry out bit (Cout). I have ...
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1answer
54 views

Parallel Prefix Adder explained

I think I have understood Carry Lookahead adders. However, I don't really understand how parallel prefix adders evolve from carry lookaheads. Can someone explain to me the difference between PPA and ...
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288 views

Verilog counter made of 32 bit adder (syntax error)

For a school assignment I have to make a counter, based on a 32-bit adder, that increments with 1 every clockcycle if 'enable = high' and 'reset = low'. When I try to use the adder in my counter ...
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1answer
130 views

problem with 6 bit adder

I am working on Subtractor circuits using Adder circuits. I have to do x-y. Suppose x = 111111 , y = 100000 Using the 6 bit adder circuit I created the overflow flag is coming to be 0 but when I ...
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1answer
505 views

Converting full adder to subtractor using inverter

I've been trying to convert a full adder to a full subtractor using an inverter. I tried using not gates at the B input ( in A B Cin ) and also using it in the outputs but the final answers are not ...
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156 views

Designing Excess 5 to BCD using Binary parallel adder

I've been trying to form a combinational logic circuit of converting excess 5 to BCD. I've been able to make a normal logic circuit but I do not know what a binary parallel adder is. My attempt - ...
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1answer
312 views

4-Bit Adder Subtractor Quartus Prime Lite

I designed a 4-bit adder/subtractor circuit in Quartus Prime Lite. I am struggling with getting the correct output on the waveform. It is supposed to take the unsigned decimal numbers and add or ...
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3answers
178 views

Why does a full adder need an OR gate?

I have read and I understand how the full adder works (or atleast I think I do :D). It combines two half adders and either one of them can have a carry over, hence the OR gate. But why do we need ...
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1answer
564 views

About the critical path of ripple adder

I have trouble understanding what's critical path delay of n-bit Ripple Carry Adder. In the book I read, given N-bit Ripple Carry Adder formed from N single 1-bit full adder: the critical path ...
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1answer
146 views

Adding multiple differential signal

As I asked in "Adding multiple analog signal" before, I got that: for adding some signal together, we can only use op-amp, instead of lovely integrated circuit (ough). But the question arise because ...
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2answers
130 views

Adding multiple analog signal

I'm trying to add 4 output of ADA8282 together and create only one analog signal with bandwidth about 6 MHz, I know Op-Amp adder as "How can I add three AC signals?" and "ElectronicTutorial" said. ...
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1answer
304 views

How do I make a double dabble circuit with logic gates

Im attempting to make a 8 bit binary calculator that displays on multiple seven segment displays. Can double dabble be done with logic gates. If so, how?
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Doubt about half adder timing

In my book there is the architecture of a basic circuit with a half adder with 1 AND and 1 XOR for the carry, and a "maimed" half adder with one XOR for the previous carry. Then book say that minimum ...
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3k views

Difference between Full Adder, Parallel Adder and Ripple Carry Adder?

I am a student and i cannot find any prominent difference between the full adder, parallel adder and ripple carry adder. The full adder for n-bit number requires n full adder cascaded, so as the ...
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How do I draw the truth table of an adder/subtractor that sets flags, and those flags are the inputs of a comparator?

How do I draw a truth table of a circuit that : starts off with a full adder/subtractor outputs the result F based on the two inputs (add if opcode is 0, subtract if opcode is 1) then output three ...
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204 views

Compare two numbers of four bits

I have two numbers both with four bits (a3 to a0 and b3 to b0 reading from left to right) and I would like to find out if a is bigger than b. I have drawn a solution of mine and a short mathematical ...
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1answer
402 views

Some questions about Carry-lookahead adder and Ripple-Carry Adder

I was reading about the Carry-lookahead adder and about the Ripple-Carry Adder. I saw some designs and it made me wonder the following questions: Both questions are the same for both adders so i'll ...
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1answer
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Formulas for Carry out in a Full Adder

Given a full adder with inputs $$A, B \text{ and } C_{in}$$ The formulas for the outputs are $$S = A \oplus B \oplus C_{in} \text{ , Where } \oplus \text{means XOR}$$ and $$C_{out} = AB + AC_{in} + ...
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Trouble with 8-bit Carry Lookahead Adder in Verilog

I'm new to Verilog programming. I'm trying to work up to a 64-bit CLA by building a 4-bit CLA, then an 8-bit (out of 2 instances of a 4-bit), then a 16-bit (out of 2 instances of the 8-bit one). I'll ...
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1answer
255 views

CMOS Adder circuits

I have been studying VLSI Design and cannot seem to find the difference between the two adder circuits below. Both implement the functionality of a full adder with Generate, propagate and kill ...
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45 views

Is parallel adder doing additions in each bit position simultaneously?

Does parallel binary adder actually make additions in each position simultaneously? I have read various sources and they all have this description relating to the parallel binary adder: "The additions ...