Questions tagged [logisim]

Logisim is a logic circuit designer for creating simple and advance logic circuits such as RAMs, Registers, CPUs, and ........

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

The image represents a 4x3 memory.Build a 2x8 memory.
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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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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 ...
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Why my register file operates abnormally

I tried to implement a 32x32 bit register file using Logisim, however once I have finished drawing and proceeded to test it by initializing the content of individuals registers to zero using the reset ...
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Finite State Machine made of JK Flip Flops in Logisim help [closed]

I'm trying to make a 4 bit finite state machine that prints out (2, 3, 5, 7, 11) in order. I have completed the next state table, flip flop transition table and the JK Karnaugh maps for all the bits. ...
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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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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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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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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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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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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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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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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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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 (...
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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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Logisim Combinational circuit

Can someone please tell me why I am getting E for an output?
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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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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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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 ...
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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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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 ...
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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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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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Logisim Flashing button

How can i create a button with a clock that is connected to a LED that the LED turns on when the button is pressed but even 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 ...
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1 answer
609 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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Curious Behavior In Logisim while trying to mimic a halt instruction

I'm in the process of trying to simulate a halt instruction based on some arbitrary value. My circuit design may not follow best practices as I'm disabling the overall or master clock sign with a ...
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How to use two Demux to index a matrix layout of registers

Consider the following. Let's say for simplicity sake I have an arrangement of 8 bit registers in a 4x4 matrix layout. I could easily use a Demux that has a 4 bit input select line for the addresses ...
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Starting and stopping of a Mod N Counter for a FSM in Logisim

I'm working on a circuit for control logic. I'm using a 3 bit down counter. There is a control signal that when it goes high starts the counter by presetting it with a value of 5. The counter is ...
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Logism shows output as X, even though the gate is connected

Below is a basic not Gate using nandgate. Not Sure why output is X, when I change it to Output properties to three state no, I can't modify circuit. Some times, these issues go away when I restart ...
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3 answers
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Implementing a SN74LS245 Octal Bus Transceivers With 3-State Outputs in Logisim

I'm testing out different circuit simulator programs and I was able to build the integrated circuit SN74LS245 Octal Bus Transceiver in a program called Digital ...
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2k views

Help making a adder/subtractor on Logisim

I have attempted to make an 4 bit Adder and Subtractor circuit on Logisim, but i've came across a problem. So the Adder works but the subtractor doesn't. When i do subtraction the 1 thats carried in ...
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8-Bit Program Counter Implementation

I'm trying to construct an 8-Bit Program Counter, in Logisim. It currently has functions LOAD, which makes the 8-Bit input (A0-A7) appear at the output (S0-S7) on the clock pulse: Loading 1 as input: ...
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