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Questions tagged [logisim]

Logisim is software for designing simple and advanced logic circuits such as RAMs, Registers, CPUs, etc.

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Which address bit width should I choose for my single cycle CPU (Logisim)

I am currently designing a MIPS single cycle CPU (32 bits) in Logisim I have already implemented the PC, instruction memory, register file and ALU. Since it is a 32 bits system I understand that the ...
Luigi_S_R's user avatar
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Shift Register 4021 Scheme

out of pure interest and a month of free time, I decided to re-create the schematics of some things I had. One of them was the NES controller. I found the schematic on the Internet and decided to make ...
Retro Enjoyer's user avatar
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2 answers
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7-segment display driver question

I believe I'm having some issues interpreting an assignment for my Digital Systems class. What I've done so far is make the segment table for the display, make a truth table for A-G, k-maps for A-G, ...
Anthony L's user avatar
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How to implement the Instruction Set in Logisim

I have an assignment that requires me to build an 7-bit CPU. I’m done with implementing some of the requirements that includes 4 8-bit registers (the requirements say I have to store the parity bit), ...
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Logisim latch oscillation issue

I would like to get familiar with latches, so I have build a circuit similar to an SR Latch. Logisim throws oscillation errors when I try to test it using different inputs. In my opinion the circuit ...
MetaLogicianWannabe's user avatar
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1 answer
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Exiting a clock loop in Logisim

I've been trying to get a traffic light simulation working on Logisim but I've run into some issues. The way the circuit works is that I default to the green light, and when I press a button (...
ramwen0's user avatar
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Implementing a circuit using only NAND-2 gates

I have this boolean expression that I got through a k-map twice, once using POS and the other SOP, and I am supposed to implement both minimized f's that I found using only NAND-2 gates but I am very ...
Salma Mostfa's user avatar
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1 answer
370 views

D Flip Flop Design on Logisim

I am trying to build a D flip-flop but I can´t get rid of those red wires. Is there a way to solve this? EDIT: I was able to fix it manually through step-by-step simulation, but I still would like to ...
dedelli_kun's user avatar
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How to get a 60 Hz frequency at Logisim? [closed]

I'm projecting a circuit at Logisim that needs a 60 Hz frequency for the clock. Looking at the Simulate tab it does not show anything like this. I even looked at the documentation, but found nothing. ...
Gabriel Shiva's user avatar
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1 answer
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How can I convert boolean algebra to logic gates?

I have a very large boolean algebra equation that I designed in Logic Friday, but it got too complicated for it to turn into gates. Note that I am a programmer, not an electrical engineer, so please ...
ShadowProgrammer's user avatar
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JK flip-flop in Logisim

I'm trying to create a JK flip-flop using Logisim, but I don't get an output. Can somebody help me find the problem?
dumb's user avatar
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(Logisim) D-flip-flop asynchronous reset not behaving as intended

I made the following 1-minute clock circuit in logisim that's supposed to count up to 59 seconds and then loop back to zero: It works mostly fine, but the problem happens when it reaches 59 and loops ...
Svedberg's user avatar
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Need help with understanding my circuit

I was wondering if anyone could tell me a little more about this: For the tests in Module 3 you need a clock generator that supplies single clock pulses with a well-defined positive (rising) and ...
Bryan C's user avatar
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3 votes
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Are there any "Both Rising Edge and Falling Edge Triggered" Shift Register?

I was designing this circuit in Logisim-evolution. In the book, it is mentioned that an n-bit multiplier would require n-clock cycles to work. I think this will be possible only when we have the shift ...
Vedanta Mohapatra's user avatar
2 votes
2 answers
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Why is this NAND gate not turning on with both inputs off?

Problem I am trying to simulate a circuit that acts like a memory bit in Logisim Evolution but for some reason the NAND gates don't turn on with both outputs set to 0. I suspect that the problem ...
Sujal Singh's user avatar
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1 answer
430 views

There's something wrong with my 2-bit adder

I made a 2-bit adder in Logisim Evolution and for some reason it gives the wrong output. I searched a ton of forum posts and all of them use the exact same design and they say it works. Here's a ...
wetturtle45's user avatar
1 vote
1 answer
199 views

How to pipeline CPU instructions in sequence?

I am designing a 16 bit CPU in Logisim Evolution. I have already designed single clock cycle instructions. I have 19 bits to control. I tried using the register and clock divider circuit to send data ...
dulatello08's user avatar
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1 answer
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Logisim - Initializing a state on a counter

Full context: I am building a stopwatch / countdown timer. The design is that there will be up/down counters that increment/decrement the time. The counters are then connected to 7-segment displays to ...
Monique_S's user avatar
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Logisim: 2 input digit lock system

I am designing a system which only have 2 input (x and y) and the system will unlock when password 10010 is entered, with 100 as y and 10 as x. The sequence of the password is from left to right. I ...
HY2000's user avatar
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3 votes
1 answer
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Glitch in circuit consisting of 2 flip flops

So I have been trying to figure this out. I made the circuit in Logism: Though I am having trouble figuring out whats causing it. From what I understand, it could be because 1 of the inputs of the ...
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Strange Logisim error; subcircuit does not work in main

I have created a subcircuit that decides if a 3-bit signed binary digit A is larger than a 3-bit signed binary digit B. It works correctly in its subcircuit file. It does not, however, work when added ...
gogo's user avatar
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Why is my Logisim circuit output xxxx?

The picture below is a Logisim circuit output. As you see, each output bit is an x, not a 1 or a 0. Is there something I should change to make the output show 0 or 1?
Kororo's user avatar
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2 answers
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Why can't I use my Half-Adder in another circuit?

Screenshot of my half-adder working like it's supposed to: I've then saved this as a circuit to use within another circuit: So why is this not working?
scarteramani111666's user avatar
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Trouble Designing an Adder that works with register in Logisim

I have designed three different modules in Logisim: Half adder, full adder, 4-bit adder below is the implementation of each of them (I am not allowed to use the program's Arithmetic folder). My ...
Milad5608's user avatar
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1 answer
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Custom D Flip Flop in Logisim Simulation Error

I am building a custom D flip flop in Logisim as a part of the project for my computer organization course and I am not allowed to use the built-in flip flops. When I designed this flip flop ...
Milad5608's user avatar
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1 answer
478 views

How do I pass the 4 bit memory address back to my RAM address input?

I'm trying to build a control unit. I'd like to pass the 4 bit memory back into my RAM. I added an extender to get 8 bits, but something seems wrong with the circuit(in red), and from the feedback ...
nvs0000's user avatar
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1 answer
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Logisim: Implementing a control unit for "Addition", "Logic bitwise AND" and "right logic shift" in ALU [closed]

I'm very new to circuit design. I've built an ALU and now I only need a control unit for three operations, "Addition", "Logic bitwise AND" and "right logic shift". What ...
nvs0000's user avatar
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Building a stepper in Logisim - Cannot find the error

I try to build a stepper based on a book. I have been looking for the error for hours now, but still could not find it. Maybe you can help me with this issue? This is my stepper: This is a working ...
MetaLogicianWannabe's user avatar
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1 answer
177 views

How to Remove Ghost Duplicate Pins in Circuit Appearance

One of my subcircuits I designed for some reason has more pins in the circuit appearance than it has in the circuit itself. In the actual subcircuit, there are 47 pins, which is the correct amount. I ...
WatsonBoi's user avatar
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Digital downcounter not resetting

I have a digital down counter which is supposed to count from 9 to 0 and then it goes back to 9 (bottom) but it only goes back from 9 to 8 and then back to 9 and I don't understand how it works. Note ...
Clone Wars's user avatar
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2 answers
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Building a 2x8 memory using flip-flops and logic gates

The image represents a 4x3 memory.Build a 2x8 memory.
Bjoni's user avatar
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1 answer
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Logisim MUX selection

I have designed a 4x1 MUX. I want to give the selection from two diferent inputs and not one 2bit input. How can I do that, if possible? In the image you see the "incompatible widths" error ...
deSYNC's user avatar
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1 answer
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Apparently correct D-flipflop implementation breaking my circuit. When using built-in D-flipflop, the circuit operates correctly

I need to design a simple 4-way traffic controller for an assignment. Traffic is from Road 1, Road 2 and Road 3 (see diagram below). If there is traffic on road 1 only, road 1's traffic light stays ...
rhododendron's user avatar
1 vote
1 answer
727 views

Why does my register file operate abnormally?

I tried to implement a 32x32 bit register file using Logisim. Once I have finished drawing and proceed to test it by initializing the content of individual registers to zero using the reset input, ...
Riccardo Raffini's user avatar
4 votes
2 answers
4k views

Logisim Help - Using Custom D Flip Flop

I am trying to create a D Flip Flop to use in a bidirectional 4-bit shift register, using Logisim. However, when using my D flip flop the shift register acts just as a normal register setting the bit ...
lilnut's user avatar
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1 answer
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Why does this give me a red wire in Logisim?

Why does this gives me a red wire? Is it a bug? I'm pretty sure my wirings are correct.
daniel123's user avatar
1 vote
1 answer
610 views

Can I implement addition and subtraction in different operations using a MUX?

I'm building a 16-bit ALU that needs to be able to perform logical AND, OR, add, subtract and rotate one bit to the left. I need to have addition and subtraction operate with different op codes ...
Matt L.'s user avatar
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4 votes
1 answer
2k views

How do I implement a rotate left 1 bit operation in a 16-bit ALU in logisim

I'm creating a 16-bit ALU that has to perform logical AND, logical OR, addition, subtraction and rotate left one bit. I have everything working perfectly except the rotate left one bit. I think I need ...
Matt L.'s user avatar
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1 vote
0 answers
685 views

Convert from 4 bit binary number to 2 bit binary number

I am currently using logisim to output a 2 bit binary number, however, the bit adder releases 4 bit binary number instead. Is there any way to fix this? (I am currently using v 2.14.6 .)
anonymouseeeee's user avatar
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349 views

Simple ROM bit cell

I was reading about ROM example from Computation Structures. Here is the ROM example mentioned in the lecture. I set up a simple circuit to understand the inner working logic of the circuit. When I ...
user avatar
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2 answers
1k views

Connecting input and output to the same bus

I'm reading "But how do it know". And in register chapter, it talks about connecting both input and output pins to a bus. I tried to do it on Logisim but it shows red wires. Can someone ...
mikal's user avatar
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1 answer
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3 digit of 7-segment on logisim [closed]

I'm working in a project, which will show an arithmetic result as a 7-segment, I know how to do a one digit 7- segment on logisim, but this makes the result limited from 0 to 9, and my project ...
Greital's user avatar
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1 vote
2 answers
498 views

Why does my synchronous up counter count enable not function properly?

I have designed a simple 4-bit synchronous up-counter, using master/slave JK flip flops in Logisim. Here is my JK design: And my counter design: It works perfectly as intended, however if the INC (...
eddiewastaken's user avatar
1 vote
0 answers
4k views

How to use VHDL Entity in logisim evolution?

I'm new in Logisim and VHDL. I'm trying to use VHDL entity-component but the output always is "x". Then I read a document ( this link ) that said Logisim requires ModelSim to use this feature. So I ...
Wachira's user avatar
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3 answers
244 views

Logisim Combinational circuit

Can someone please tell me why I am getting E for an output?
icecold's user avatar
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2 votes
1 answer
3k views

Is A XNOR B logically equivalent to A XOR (NOT B)?

I am just wondering if its fair to say that A XNOR B is logically equivalent to A XOR ~B? If yes, how do I justify that without a truth table?
alwaysconfused's user avatar
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1 answer
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Clearing 4-bit asynchronus counter using T flip-flops doesn't work

I am trying to make a BCD ripple counter that count from 0 to 9 , and I have watched a tutorial on YouTube , I implemented BCD counter as the instructor explained and after the counter reaches the ...
NAND's user avatar
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1 answer
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3 Bit Adder Logic Circuit Design

Im trying to design a logic circuit for a 3 bit adder using 6 inputs, A2, A1, A0, B2, B1, B0 and 4 outputs, s0, s1, s2 and c (the carry out). I already have circuits for a half adder, full adder and a ...
alwaysconfused's user avatar
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1 answer
2k views

Displaying 6 bit numbers on two 7-segment displays

I designed 6 bit binary adder which should add two numbers in first complement. The numbers are being input via registers. I have to display the numbers and the result on two 7-segment displays via ...
ChidoriMaster's user avatar
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983 views

Counter Circuit starts from wrong number in Logisim

I'm trying to design a synchronous counter using J-K, T and D flip flop. It should count as "1, 3, 0, 2, 7" and 1 respectively. Everything works fine, i designed flip-flop tables and input-outputs ...
Hasan Muzak's user avatar