Questions tagged [logisim]

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

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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?
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1 answer
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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 ...
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2 answers
105 views

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 ...
3 votes
2 answers
186 views

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 ...
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40 views

How to expose a bus to multiple pages in Logisim Evolution

Let's say I have a piece of RAM that I want to expose everywhere in my circuit. I.e., I want to design on multiple pages, but always have access to the RAM address bus, data bus and clock lines. I ...
2 votes
2 answers
868 views

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 ...
1 vote
1 answer
66 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 ...
1 vote
1 answer
81 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 ...
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1 answer
319 views

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 ...
1 vote
0 answers
191 views

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 ...
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2 votes
1 answer
318 views

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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1 answer
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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 ...
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235 views

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?
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-3 votes
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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?
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2 answers
579 views

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 ...
1 vote
1 answer
660 views

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 ...
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1 answer
307 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 ...
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-1 votes
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 ...
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1 vote
0 answers
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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 ...
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1 answer
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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 ...
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307 views

Designing subtractor using adder in Logisim for 1-bit ALU. How to implement Multiplier in my 1-bit ALU?

How can I design subtractor using adder in Logisim for 1-bit ALU (Arithmetic Logic Unit)? And also, how can I implement Multiplier in my 1-bit ALU? Here I tried to make 1-bit ALU which will perform ...
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1 answer
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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 ...
-4 votes
2 answers
399 views

Building a 2x8 memory using flip-flops and logic gates

The image represents a 4x3 memory.Build a 2x8 memory.
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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 ...
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1 answer
511 views

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 ...
1 vote
1 answer
440 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, ...
3 votes
2 answers
2k 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 ...
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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.
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84 views

4 address lines for 1 bit input

I am currently trying to design a 16 nibble RAM on logisim, whereby it takes 4 data input lines. However, what I am having the most trouble with is converting the 4 address lines into a single input, ...
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1 answer
310 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 ...
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4 votes
1 answer
1k 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 ...
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1 vote
0 answers
406 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 .)
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Counter with 4 flip flops jk synchronous from 1 to 12?

I wanted to create a circuit that would count from 1 to 12 to make hours counter for the digital clock. I work on logisim. I already made counter mod 13 but don't know how to adjust from 1 to 12 (not ...
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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 ...
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2 answers
773 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 ...
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1 answer
2k views

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 ...
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1 vote
2 answers
331 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 (...
1 vote
0 answers
3k 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 ...
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0 votes
3 answers
160 views

Logisim Combinational circuit

Can someone please tell me why I am getting E for an output?
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2 votes
1 answer
2k 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?
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1 answer
413 views

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 ...
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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 ...
0 votes
1 answer
1k 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 ...
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1 answer
668 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 ...
1 vote
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Do these two memory register diagrams look correct?

So to start this off I have used J-K flip flops instead of D flip flops due to the equipment that I'll be using (Logic Tutor LT345 Mk2). The first diagram I am confident is correct but the 2nd diagram ...
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4-Bit ripple down counter using negative edge-triggered J-K flip flops

Ok, so as the title says im wanting to build a 4-bit ripple down counter on logisim so that I can find what 15 in binary is along with what 9 in binary is to make a mod-10 ripple down counter. But how ...
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908 views

4-bit memory serial to parallel memory register circuit question

I am building a 4-bit serial to parallel memory register and I feel like so far I have gotten things right, but I'm unsure of where to connect the CLR connections. Could someone have a look at my ...
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1 answer
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Logisim flashing button

How can I create a button with a clock that is connected to a LED so that the LED turns on when the button is pressed, but if you keep holding it it will turn off?
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Designing a cryptographic S-Box in Logisim

I am currently working in Logisim and was wondering if I can design some ciphers in the same. One such cipher is PRESENT cipher which is essentially a block cipher. I did get that I need to design the ...
1 vote
1 answer
689 views

How to get the IC numbers of the logisim items

Logisim makes it very easy for user to intuitively manipulate and edit the components already provided to achieve the circuit he wants. But there is no information ...
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