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# 4 bit simplest digital computer

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#### Avidestroyer

##### Junior Member level 2
Hi all. I am new here and also biginner in electronics. I want to make a simplest digital 4 bit computer. Is it possible. Plz help anyone with me

Check out Xilinx's microcontrollers picoBlaze that use a small amount of CPDL gates. Ok it is 8 bits, but that is handy for a reasonable amount of address space. 8 bits it more useful because it takes two 8 bit additions for a 16 bit total addressing calculations using central 8-bit ALU. 4-bit ALU would need 3-4 chained additions to make useful address space.

What is CPDL?

Hi,

A simple google reveals this circuitry which matches what you ask for.
https://www.waitingforfriday.com/index.php/4-Bit_Computer

That video teaches you some good fundamentals, but it would be a long job to build that circuit just to prove what it teaches.
There are software simulation programs that could easily do the same as any hardware.

You can also follow on those basic functions by many of the online tutorials / ytubes.

I have already notice this(waiting4friday). But it just a description about ALU. So I want to learn that how to make a simple CU and RAM and how to interfacing these with ALU?

I have already notice this(waiting4friday). But it just a description about ALU. So I want to learn that how to make a simple CU and RAM and how to interfacing these with ALU?

Hi,

Not sure what you are trying to do /achieve ?

Your reference to a digital computer could be interpreted in many ways.

You might find some retro sites on building old ic type computers like Z80s, but the cost and physical complexitiy of building one from transistors or basic logic gates simply is not practicable.

Rather than trying to recreate 50 year old machines why not learn some of todays simpler micros like the Pic 16F range which you can equally use to demonstate everything from simple logic functions to complex operations, by utilising both hardware and software examples.

What is z80?

Z80 and Z81 are Computers of 80's era. It uses Z80 mpu. Search for \$-bit ALU in google. You will get the diagram of Intel 4004 ALU which is 4 bit.

go to year 1971:
https://en.wikipedia.org/wiki/Word_(computer_architecture)
and click on Intel 4004 - 4bit computer!

- - - Updated - - -

and very interested presentation of 4bit computer:
https://www.randelshofer.ch/fhw/gri/holzihelp.html

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