What do i need to know to build a 8 bits computer?

[cmb]

Hello,

 

I am very interested in building a simple 8 bits computer and i would like to know what do i have to study to build one.I think i will save much time asking this question.

I am using a circuit simulator, i think it would be useful.

 

Thanks!

[Endy0816]

Logic Gates, Adders, Memory, Clocks.

 

Have you worked on any similar projects before this?

[Klaynos]

How basic do you want to go?

 

If you understand gates all you need is a lot of dominoes...

 

https://en.m.wikipedia.org/wiki/Domino_computer

[studiot]

The first modern generation (VLSI integrated circuit) digital computers of any note were 4 bit.

These were used by the professionals of the day to start and they still are used for simple computer control circuits such as for washing machines etc.

 

So 4 bit might be a better place to start.

 

8 bit chips brought in the age of the desktop computer and eventually the PC.

 

Also at this time the multilayer model came in.

 

So you have

a hardware layer

a functional block layer

a machine code or program layer

a higher level code layer

a an applications layer

a user layer

 

and so on.

 

You need to become familiar with the term bus, where several individual connections are treated as one (parallel bus, serial bus, data bus, memory bus, control bus etc).

 

Most people think of a microprocessor as a single chip. In fact 'it' is often several chips carefully matched to provide the required functionality of input/processing/output. Collectively, these are called a chipset.

Chipsets contain all the necessary gates and other logic stuff to achieve the requirements, ready configured.

So although it may be desireable to learn low level digital logic it is not essential.

You simulator will have several chipsets available if it is any good.

 

A computer is only useful if you can get it to run ie do something.

 

For this you will need to study low level programming or machine code and assembler language or better since some modern chips come with a form of BASIC built in.

 

So what part of of the multilayer diagram are you most interested in?

[John Cuthber]

My brother built on decades ago based on a book like this

http://www.amazon.co.uk/How-Build-Your-Working-Microcomputer/dp/0830612009/ref=asap_bc?ie=UTF8

[cmb]

That's the first time I work with hardware.I already know programming, what's logical gates and make basic operations with binary.I am just doing that for fun, the computer will calculate some basics operations.

 

 

Thanks for helping

[Strange]

This looks like it might provide a good intro to the basics of computer architecture: http://www.aw-bc.com/info/carpinelli/

It even has a sample chapter which might cover what you need to know: http://www.aw-bc.com/info/carpinelli/

What sort of circuit simulator are you using? What language does it use?
You really need a gate-level (logic) simulator, not a transistor-level (analog) simulator. Idealy, it should be possible to use a standard hardware description language (HDL) such as VHDL or Verilog. (VHDL is obviously far superior, but for some reason Verilog appears to be more popular). Or it might just have a graphical user interface.

This paper gives an overview of the steps involved (but doesn't have much detail): http://db.grinnell.edu/sigcse/sigcse2013/Program/viewAcceptedProposal.pdf?sessionType=paper&sessionNumber=39

This paper describes a sequence of assignments, each building
upon the next, leading students to a working simulation
of a simple 8-bit CPU (Central Processing Unit). The design
features a classic Von Neumann architecture comprising a
simple data path with a few registers, a simple ALU
(Arithmetic Logic Unit), and a microprogram to direct all
the control signals. The first step involves the design of the
ALU which is capable of eight basic operations. The second
step guides students to construct a datapath complete with
several 8-bit registers. The third step involves the design
and implementation of a control unit which uses a microprogram
to implement machine code instructions. The microprogram
implements nine basic machine language instructions which
are sufficient for writing many simple programs. The final
step involves adding program memory and an input and
output device to form a simple working simulation of a
computer. At this point, students may hand-assemble code for
their CPU and simulate its execution.
All simulations are performed using a free and open source
simulator called Logisim which performs digital logic
simulations with the ability to build larger circuits from small
er subcircuits. Students can set an adjustable clock rate and
observe the internal CPU state and registers as it retrieves
instructions and steps through the microcode. The basic
CPU architecture provides many opportunities for more advanced
exercises, such as adding an instruction fetch unit,
adding pipelining, or adding more machine language instructions.
The assignments were introduced in a second year
course on computer organization, providing an effective hands-on
approach to understanding how a CPU actually operates.

The simulator they use is available here: http://www.cburch.com/logisim/

There are some brief reviews of some other simulators here: http://web.eng.fiu.edu/watsonh/eel4709/MSP430/CPUSimulation/TeachingCompArchitecture.pdf

[Sensei]

That's the first time I work with hardware.

Then IMHO you should start from something simpler.

Make f.e. LED counter, going from 00 to 99 for instance.

 

Have hardware register in binary format (some use binary coded decimal, and BCD addition, 8 bits = 2 digits each one with 0...9 digits, 10..15 values in 4 bits not used),

that's converted to decimal format,

which is later used to turn on/off LEDs forming digits.

 

It's plentiful of work IMHO,

see how complex breadboard he has on this video:

 

ps. For a start I would try making radio receiver playing music by speaker. It's easier to make than LEDs digital counter. Start from generating sinusoid wave for speaker from oscillator/timer. That you can adjust with potentiometer. Amplifier that takes microphone input signal, amplifies it, and sends to speaker in f.e. 2nd room. Then adding part for radiowave receiving will be just piece of cake.

Edited September 15, 2015 by Sensei