# Logisim 8 bit computer system project

#### Zerokill

Joined Dec 10, 2015
6
Hello and thank all of you who read and respond to this post. I only have logisim, due to my wealth meter if not free I can not use the tool. I am trying to build a game console simulated. I do not know if the text books here cover what I need to know, if they do please direct me where and to the correct tome of text. I know a lot, yet I know little in the subject I am doing, I do not want to go FPGA off the back, I may go that route later I want old school I understand logic gate and nand or nor not buff for nxor how they work with two inputs unless buff or not of a one input. I understand ttl of buff and nand gates only in CMOS. I can use clarify in that I know I need RAM and I/O ports in operations an alu that does the binary math actions a gpu, rom. I have an idea of what a register is and an accmlator and a decoder mux encoder but love more clarity. I like to understand how to not solve Boolean exsprsions but how and why I need them to make what I am doing and how to do math better. I know I need to build a OS thought assybly and since small room of 256 of ram. I feel as if I am in a whirlwind of bits of what I need to know and like guidance to basicly ttl my logic gates to build logic gates then my gates to build all my parts in IC's then to connect or distribution and condince the logic I guess in kmaps need help in learning it right and with wird wrap arounds. Then take that and build OS looking to make this simple so I can expand on this into 64 bit but focus on this to get my self well grounded, hehe grounded in this. If a four bit would be easier I welcome this becuase I can just dubble it and give half men and other lsb operations and have it 8 bit from a 4 bit split like ram or am I way off. What is the major difference between latch and flipflop if I put a feed back on a latch would it be easier to latch than flip-flops at least in parts but maybe not in control of pulse counting idk. I need help in clarity in this subject and to emulate it in logisim. I am very happy with any input in any part or parts of my goal that you are able to assist or advise with. Note simple but connective in responses please I have autism and I may ask questions to something that may be well rooted to its smallist or simplified version of a question on its answers. How I think like you give an algebra exsprsion simplified then I would want to turn it into a polynomial and work it from there kind of guy so thanks for your help and willingness aswell patience with me.

#### sailorjoe

Joined Jun 4, 2013
363
On this web site there is a book about digital logic. http://www.allaboutcircuits.com/textbook/digital/
Learn all of it as a starting point. The book covers a lot, but doesn't tell you how to design a computer from scratch. However, the lessons are required in order to understand what they're telling you about how to design a computer.
If you start a design, start with a four bit computer. Its easier to handle, by a lot. I've done it, and limited myself to just nand gates, as a challenge. Read about CPU design; it's a whole field of study in itself.
If your goal is to build a game console, then consider starting with a complete computer like an Arduino or Raspberry Pi, or PIC. Learn to program them in assembly language, and you'll have a much deeper understanding of how a computer works deep down inside. And you'll also be able to get your game working much sooner.

Ok, I just realized that your goal is to build a simulated game console on logisim. Maybe if you tell us about the game you want to design, we can get started. Games like PONG and PACMAN can be done with "old school" logic gates. PS3, not so much.

#### Zerokill

Joined Dec 10, 2015
6
Thank you, I am interested in pong is okay I like to work up to Mario Bros ablity, and I have an ardino uno but I know nothing in c or assembly I love to learn both. Why I want to emulate is my \$ is limited to zero so why I want to use logisim and then I can get it going in real life on a FPGA by logic gate the whole thing but yeah that once I get going on cpu design it should not be as hard but interesting. do to my brain hard is easy and easy is hard, I am excited to work on such projects that really makes use of my mind and with technology masters that aid me on my journey so thank you.

#### absf

Joined Dec 29, 2010
1,949
Making an 8-bit Computer on a simulator like logisim and be able to program mario brothers are two different types of project.

Is logisim able to simulate simple 8 bit RAM or ROM? Without that ability, your final computer would not be able to run the simplest program on your simulator. I have done one on proteus making a 4 bit TTL CPU using 25 TTL chips. Later I found out that proteus doesn't support static RAM and ROM. So it didn't work in proteus but it worked on real hardware.

Here is one very cool 4 bit computer that I intend to make. It is called Nibbler 4 bit cpu and the web site is here. It is very well described on its working, block diagram and also schematics. Once you understand how it works, you can start simulating it on your simulator or build it...

Someone has also made it into a nice PCB if you just want a working version.

Allen

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#### Zerokill

Joined Dec 10, 2015
6
It should people can play astroids and pong and make gpu but I don't really know since I am new to logisim I know it does not emulate at true clock speeds I believe thank you for your input.

#### Zerokill

Joined Dec 10, 2015
6
Thanks for your message, I think it can be done since pong and astroids can be simulated, but this is a project to get me familer before I go hog will d with a more depth project.