How do I make a 8 bit computer?

How do I make a 8 bit computer?
Posted by wintech on 08 Aug, 2019 10:12
Hello, I know this is a very stupid question but how do I make a 8 bit computer?What do you recommend for a beginner in 8 bit computers?

#1 Reply
Posted by wilfred on 08 Aug, 2019 10:28
I would start here http://searle.hostei.com/grant/z80/SimpleZ80.html

Usually someone wanting to do this is feeling nostalgic and already knows the microprocessor chip they intend to use. I was Z80. Some go with 6502 or 6809. The only advice I would give to someone who hasn't decided is to ignore anyone who starts to try convincing you one is better than another.

The Z80 has the CP/M OS and that has quite a bit of software available. I'm less familiar with others. For a long time I was tempted by the 6809 and OS-9.

The first step is to pick the CPU. To do that i'd recommend finding the software that appeals.

#2 Reply
Posted by alanb on 08 Aug, 2019 12:27
It depends on whether you want to use a microprocessor or build it using 74 series logic gates. If you take the logic gates route it's worth watching the U Tube videos by Ben Eater on this topic.

#3 Reply
Posted by woofy on 08 Aug, 2019 12:56
Ben Eater's videos are the best I've seen for a make it yourself 8-bit computer.
https://www.youtube.com/channel/UCS0N5baNlQWJCUrhCEo8WlA

#4 Reply
Posted by GK on 08 Aug, 2019 13:04
Just buy some breadboard and a big reel of solid-core wire.

#5 Reply
Posted by Nusa on 08 Aug, 2019 13:30
If you want theory and design, I recommend the following book, which is now available digitally for free:
https://www.academia.edu/36492595/Prosser_The_Art_of_Digital_Design_2ed

Plus it includes a tested (in lab courses) non-commercial design for building a PDP-8 using TTL. That's a 12-bit computer, not an 8-bit one. It was a commercial success in its day (1965 to maybe 1980) and likely predates whatever 8-bit computers you were thinking of.

But it all depends on what you are looking to learn.

#6 Reply
Posted by woodchips on 11 Aug, 2019 10:03
Or try Build a Microcomputer or Bit Slice Microcomputer Design by Mick and Brick of AMD.

How to make a computer using the 2900 series parts, but much of it will carry over to using the 74181 and similar.

#7 Reply
Posted by shawty on 22 Aug, 2019 19:50
Quote from: alanb on 08 Aug, 2019 12:27
It depends on whether you want to use a microprocessor or build it using 74 series logic gates. If you take the logic gates route it's worth watching the U Tube videos by Ben Eater on this topic.

I second "Ben Eaters" channel, he really is rather excellent in his content. His last 2 videos he built his own VGA card using nothing more than Cmos counter chips and an eeprom!!!

#8 Reply
Posted by mindcrime on 23 Aug, 2019 01:51
https://www.amazon.com/Build-Your-Own-Z80-Computer/dp/0070109621/ref=sr_1_1?keywords=build+z80&qid=1566525068&s=books&sr=1-1

#9 Reply
Posted by hamster_nz on 23 Aug, 2019 02:01
If you want to build a computer, not build an 8-nit CPU, then a RC2014 is worth looking at.

https://rc2014.co.uk/

#10 Reply
Posted by Psi on 23 Aug, 2019 02:06
Quote from: wintech on 08 Aug, 2019 10:12
Hello, I know this is a very stupid question but how do I make a 8 bit computer?What do you recommend for a beginner in 8 bit computers?

To start learning and understand the concept, think about having the following
-A fixed 8 bit number
-Another fixed 8 bit number
-A 8 bit adder circuit
-Three 8 bit 8 stage shift registers. (3 separate bytes, 8+8+8=24 shift registers)

Now think about how you can clock all the shift registers together to make each byte step through the system on each clock.

Now think about how you can have one stage of the shift register load each of the two fixed numbers into a byte of the shift register.

Now think about how you can have one stage of the shift register use the adder to add two of the current bytes and put result into the current 3rd byte.

Expand from there.

#11 Reply
Posted by shawty on 23 Aug, 2019 09:49
Also I find this:

https://github.com/hneemann/Digital/releases

is fantastic for prototyping.

It also has a great component API written in Java (I've written a 6522 VIA component) which means you can actually model your chips in software, and then build circuits around them.

Shawty

#12 Reply
Posted by granzeier on 23 Aug, 2019 10:57
Quote from: mindcrime on 23 Aug, 2019 01:51
https://www.amazon.com/Build-Your-Own-Z80-Computer/dp/0070109621/ref=sr_1_1?keywords=build+z80&qid=1566525068&s=books&sr=1-1
A great book, a classic. Unfortunately, very high priced, on Amazon. You can also download a copy (Steve Ciarcia - the author - has released it) from: https://ia800109.us.archive.org/4/items/BuildYourOwnZ80ComputerSteveCiarcia/mVQnFgWzX0AC_text.pdf

#13 Reply
Posted by granzeier on 23 Aug, 2019 11:01
Quote from: shawty on 23 Aug, 2019 09:49
Also I find this:

https://github.com/hneemann/Digital/releases

is fantastic for prototyping.

It also has a great component API written in Java (I've written a 6522 VIA component) which means you can actually model your chips in software, and then build circuits around them.

Shawty
Shawty,
Thanks for this. It looks like Logisim; do you know the differences (other than Logisim development having been dropped)?

#14 Reply
Posted by shawty on 23 Aug, 2019 14:04
Quote from: granzeier on 23 Aug, 2019 11:01
Quote from: shawty on 23 Aug, 2019 09:49
Also I find this:

https://github.com/hneemann/Digital/releases

is fantastic for prototyping.

It also has a great component API written in Java (I've written a 6522 VIA component) which means you can actually model your chips in software, and then build circuits around them.

Shawty
Shawty,
Thanks for this. It looks like Logisim; do you know the differences (other than Logisim development having been dropped)?

It pretty much is Logisim. The author took the original Logisim code and re-wrote most of it to newer code standards after the original Author walked away from the project.

The internals of the code are vastly different however, but the great news is, the API for creating your own Java Components is so much simpler than the original.

I don't actually know if it's compatible with the original Logisim file format, I have to admit I never tried I just created most of what I had saved from new. The UI is mostly the same, as are the components, but digital has the ability to interface to a VHDL system which Logisim never could.

Components written for the old one won't work in the new one, that much I definately know. I thought I'd uploaded all my components to GitHub (http://github.com/shawty) but I havent, for now however the 6522 VIA I was on writing can be found in the issue where myself and the author of digital had a good conversation going on how to implement two way I/O: https://github.com/hneemann/digitalCustomComponents/issues/3

Shawty

#15 Reply
Posted by pcmad on 03 Sep, 2019 01:03
i got a z80 and supporting chips if you want to buy them off me based in uk

#16 Reply
Posted by Kean on 03 Sep, 2019 07:17
Quote from: pcmad on 03 Sep, 2019 01:03
i got a z80 and supporting chips if you want to buy them off me based in uk

Please stop posting the same things in multiple topics.

#17 Reply
Posted by GVC96 on 20 Oct, 2019 01:30
If you're building a CPU out of logic chips and discrete components I would recommend creating your own instruction set because you would be able to tailor it to an easy hardware implementation, plus you can omit the more difficult(number of chips and connections wise) to implement features like interrupts and what not. Making an instruction set isn't really hard, you mostly just decide what registers you'd like to have and what you'd like the opcodes to do.

If you want to build a computer using a microprocessor or microcontroller I would recommend something like the atmega1284p, the instruction set is elegant and orthogonal for the most part, it has 128k flash and 16k ram, which is plenty and would save you the work of hooking memory up to a microprocessor. It also supports self-programming so you could even write an assembler to run on the chip and then write it's output to flash and execute it so you could program it in system.

#18 Reply
Posted by granzeier on 21 Oct, 2019 14:33
Another classic book, which has been released by its author, is Jan Axelson's "The Microcontroller Idea Book" (http://janaxelson.com/files/microcontroller_idea_book.pdf) - it is actually being hosted on her web site.

The 8052-BASIC system that she describes can actually be pretty simple. Her first schematic (figure 3-1, page 24) contains only seven chips. If you have a TTL USB-to-serial converter, don't need to expand beyond 32K of RAM, and don't mind a slightly sloppy reset (use hers without the diode and 74HC14 inverter, it will work fine) you can build a BASIC computer with only four chips. Of course, Jan goes on and adds a bunch of additional stuff - the BASIC-52 computer can be expanded just like any other computer.

#19 Reply
Posted by Flenser on 22 Oct, 2019 12:56
Quote
I would start here http://searle.hostei.com/grant/z80/SimpleZ80.html

The link above no longer works. That page is now under this new domain http://zx80.netai.net/grant/z80/SimpleZ80.html

#20 Reply
Posted by Flenser on 22 Oct, 2019 13:40
wintech,

You'll need to provide some more detail about what you would like to do.

If you want to get all the parts yourself and put them together, perhaps on solderless breadboards, than I vote +1 for wilfred's suggestion to use one of Grant Searle's designs. The 7-chip Z80 page is now at http://zx80.netai.net/grant/z80/SimpleZ80.html and there are links to Grant's other low chip count designs for the 6809 and 6505 chips if you'd prefer to use one of them instead of the Z80.

The advantages of using Grant's design are:
- the smaller the chip count, the simpler it will be to wire it up without error
- Grant includes the ROM basic image that you can download. Program that into an EPROM and you can start using your 8-bit computer.

If you want to start using your vintage 8-bit computer after you assemble it and you are not setup to program EPROMs then consider a kit like one of these RC2014 kits
https://www.tindie.com/products/semachthemonkey/rc2014-mini-single-board-z80-computer-kit/
https://www.tindie.com/products/semachthemonkey/rc2014-micro-single-board-z80-computer-kit/

The RC2014 page that describes these designs is https://rc2014.co.uk/ and there are links in the left-hand pane to those mini and micro kits.

The advantage of using a kit is:
- You get a set of parts provided that will work together. If you buy them yourself you have to do the investigation to get the right spec parts
- You get a PCB so are much less likely to need to debug your wiring
- You get a pre-programmed ROM chip. You don't need to be setup to program EPROMs yourself.

Going one step further you can get one of these type microprocessor trainers. These are for learing to program the microprocesser.
This link is someone who sells them as kits. I''ve not used one of these so I can't tell you if they are any good.
https://www.ebay.com.au/sch/m.html?item=283624635789&hash=item4209587d8d%3Ag%3ASjwAAOSwXeJXeMWT&_ssn=kswichit&_sop=15

I bought a Micro-Professor MPF-I trainer https://en.wikipedia.org/wiki/Micro-Professor_MPF-I many years ago to start learing Z80 assembler, which I why I've included a modern example of that type of kit.