# Tagged Questions

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### Anyone remember a rotary dial adder project from the early 1980s? [closed]

When I was a kid in the early 80s in the US, I remember coming across a published electronics project that involved a rotary dial from a telephone and small lamps, which I think was a simple adder. I ...
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### Verilog 8 bit adder & testbench - not working

Resolved - After making it compileable in Quartus by naming the for loop in my8bitadder and doing Greg's fixes, the code works fine now. Thanks guys! I've made an 8 bit adder but I can't seem to get ...
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### Display Double Digit Numbers on 2 seven segment displays

I'm making an Arithmetic Logic Unit(ALU) for an assignment and I'm on a point. So according to my circuit design on the link shared below, I am able to output 1 digit of my alu. It is a 4 bit ALU so ...
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### Adder tree with 4:2 compressors. What to do with Cout?

I'm trying to build an adder tree using 4:2 compressors. I want to add together 16 bytes at total, so I figured that a possible architecture for that tree is the following: Each 4-Byte adder has 3 ...
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### Showing negative numbers in Verilog

I am writing a program for a 16-bit ripple carry adder and stumbling a little at the end. When I run my code (which includes negative numbers), it's doing the math right, but giving me all positive ...
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### Use of D flip-flop in Serial Adder

In the circuit of a serial adder (below), what exactly is the function of the D flip-flop? Since its characteristic equation is $Q^+ = D$, couldn't it be simply removed (replaced with the wire) ...
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### IEEE 754: Rounding in an adder

Now I am trying to build a Floating Point Unit (FPU) using Verilog. After studying the rounding methods in IEEE 754, I understand that there are three internal bits(G - Guard, R - Round, S - Sticky) ...
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### Simple binary adder works only partially

LATER EDIT: 1. I've also investigated visually the Kintex7 device after implementation (i.e. interconnections, etc.) and everything looks OK - no connections that would indicate things would not be ...
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I want to implement some kind of event counter in my FPGA design (Vendor-A or Vendor-X). I have several dozens of signals: half are 1-bit and other half of them is 5-bit. Signals are located in ...
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### Multiplying 3 bit number using 4 bit full adder

So I'm trying to design a circuit where a 3 bit input can be multiplied by a constant value, for instance 6. And I'm trying to implement this using a 4 bit adder which generate a 5 bit binary number ...
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### Full adder (FA) base 8(Octal)

Please give me some help or tip about this question, I need to make a simulation of this on proteus: " Using full adder(FA) design a adder for numbers in base 8(octal) 6(8) + 4(8) = 12(8) " As ...
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### 8 bit adder with 2 CLA

I need to make an 8 bit adder with 2 4-bit look ahead adders.I spent a lot of time reading about it and I think I get the gist of how it works, but I can't seem to get this. I spent a lot of time ...
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### Multiplier 4-bit with verilog using just full adders

I am trying to write the test bench part but I don't know how to do it. Basically, I want to test out 0x10 or 5x5. I don't if what I have is right. here's a pic to give you some idea of what i am ...
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### Which gate is better in buildiing the Full Adder ? XOR or OR

So this is question asked in one of the exams. As you know there are 2 ways to get the boolean expression for the Sum of the fully adder Given X and Y are inputs, C0 is the carry from previous adder ...
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How would you find the number of clock cycles it takes to produce sum, the carry out, and overflow flag using ripple carry or lookahead adder. Can someone please explain me how would we go on finding ...
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I am trying to implement the verilog code using generate statement.There is issue with taking four bits for calculating P and G values.Added the code below for reference. Cin is taken as Zero. ...
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### Design an ALU that only adds

I need some help designing a simple ALU that only can add (4-bit) numbers. For the design I can only use 4-bit full adders and 4-bit edge-triggered flip-flops. I am stuck as I do not even know where ...
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### VHDL serial adder test bench return UUUU

I've designed some week ago this serial adder, then i let it go for a while and now i would like to state if it works or not... So the design is this one this one And i report to you the testbench i'...
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### How does Instruction Code tell an automated adder what to do? (Charles Petzold Code book, Chapter 17 Automation)

I'm reading Chapter 17 of Charles Petzold book Code (which is excellent) and in it he's describing an automated adder which he's adding different Operation Codes or Instruction Codes. In the diagram,...
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I've a design problem in VHDL with a serial adder. The block diagram is taken from a book. Since i'm not skilled enough in design with clock (except some silly flip flop i've found on the web, and ...
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in order to explain how to a pipelined multioperand adder could be implemented my book shows the image reported below. The idea is to use three adder with 4 stage pipeline. However i tried to make a ...
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### Implementing this Full Adder circuit

For my class, I have to implement the following circuit on a breadboard but I don't really have an idea on how to start. Basically, I have a 4-bit Full Adder and I will input two 4-bit binary numbers ...
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### 4 bit subtractor using 2's complement of an adder

currently having problem with my carry in to carry out. i have used this for my LSB assign S=A^(~B+1)^Cin; assign COUT=(A&~B)|((CIN+1)&(A^~B)); and this for my 3 higher bits. ...
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### Is there a way to count the number of high inputs with logic gates?

I have $2^n$ inputs $a_{0}, a_{1} .. a_{2^n}$, these can be either hich or low, and $n$ outputs $z_{0}, z_{1} .. z_{n}$, these give out a binary number of how many of the inputs are high. Is ...
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### Half Adder Using 4069 and 4011 Chips

I am having trouble designing a wiring diagram for a half adder using the following two chips: CD4069 (hex inverter) HEF4011 (quad 2-input NAND) Can someone guide me in the right direction?
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### VHDL - Cheapest-Fastest unsigned to signed binary number converter

We know that to convert unsigned to signed (precisely, I want to convert a pure binary into CA2 number) we must negate the unsigned number adding, then, + 1. In VHDL I can implement an inverter and an ...
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### My output in verilog is high impedance all the time. Why is that?

I am new to verilog and I have been writing code for 4 bit adder/substractor in structural model. My values of x0,x1,x2,x3,c1,c2,c3,cb and ...
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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"?
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I usually only become a passive reader in this forum, but today I decided to ask my first question. How many logic gates required for a 4-bit Carry Look Ahead adder and Prefix adder? I know that ...
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### Working with borrow save signed digit arithmetic output mismatch

I am working with OLA adders the borrow save module for signed digit addition I implemented the added in vhdl modeling the following picture I have run the following example as given in the table ...
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### Why is a half adder implemented with XOR gates instead of OR gates?

Half adder circuits are implemented with XOR gates for the summing. Why can't the adding function be implemented with OR gates? What is the difference between using XOR gates and OR gates?
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I would like to make a 8 bit adder, with carry look ahead, but i only have 2-input logic gates. All I've heard about use some at least 4-input gates. Or do I need to use a totally different method, ...
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I am researching memristors, and one application that's frequently cited is a crossbar latch that sandwiches memristors between two layers of wires to form a grid. In most examples, this is configured ...
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### How to use an H-clock tree in a pipelined adder

This is for a lab at my university. Normally I don't have a problem with these things, but this one is poorly written and the professor hasn't discussed the H-clock tree, which is where I'm getting ...
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### Half Adder and Two Function, A Contest Questions?

I ran into a 2013 contest question on computer-science filed. What is the following True about F and G function. (The output ...
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### Implementation of 4-bit subtractor

How to implement subtractor of two 4-bit numbers using subtractors of two 1-bit numbers as a module(no assembler coding, just expressions in boolean algebra)? If there are four 1-bit subtractors, how ...
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### How to make 2 bit or more half adder circuit

I have no idea about electronics, this semester school gave us a strange and confusing lecture about circuits which we shouldn't take because we are no engineer or something close. Question is we ...
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Are binary adder and parallel adder same thing? I couldn't find any information about parellel adder in my book. Does anybody have an idea?
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### adding two 64-bits number with m-bit carry ripple adder and multiplexer, a questions?

I ran into a question from computer architecture class. The professor says that for adding two 64-bit numbers A and B we use m-bit carry ripple adders and multiplexers such as following: and that ...
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### Using iSim to simulate 16-bit CLA schematic on Xilinx, all inputs and outputs on the waveform are 'X'. How can I debug?

I'm building a sixteen bit Carry Lookahead Adder for my EE class. I'm definitely a noob to all this so bear with me, however I've been googling for a WHILE and haven't found any answers. Here is the ...
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### Muxes, Adders, Comparators, and Gates

This question is actually from one of my previous discussions, which I still don't understand how to implement. The goal is to use abstraction to design a circuit, which converts two-digit ASCII ...
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### Bit Slice Checker

I'm attempting to use bit-slice design, to implement a circuit which checks if an n-bit binary number A has an even number of 1's in its binary representation. I've decided that the circuit should ...
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### Which 4-bit Binary Number Is Greater?

My Task I'm working on an extra work question our teacher assigned us from the book. Design a combinatorial circuit that compares two 4-bit unsigned numbers A and B to see whether B is greater than A....
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### What would be the output of A = 0100 and B = 0111 with S = 1 in a 4-bit binary adder-subtractor?

I understand S = 1 means subtraction and S = 0 means addition. So then, the output would be the result of 0100 - 0111. But since it's negative, I'm not sure how it would be represented. I know the ...
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How can I find Gate Delay for bit 1 of the sum by a 4-bit look-ahead carry adder?
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### Design a full adder of two 1-bit numbers using multiplexers 4/1

How can i implement the full adder of two 1-bit numbers using only multiplexers 4/1? I created a truth table for a one-bit full adder, which looks like this: A = first bit B = second bit Pu = bit ...
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### Batteries in parallel vs voltage signals in parallel

From a practical point of view, when you connect two audio signals to one speaker the result is that both audio signals can be heard. That means the two voltage waves were added, correct? However, ...