
8-bit computer from scratch - danielam
https://ciernioo.wordpress.com/
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Animats
Hint: when posting images of schematics, make them big enough that readers can
zoom in and read the numbers.

It's interesting to see this done with so few ICs. Early Z80 machines had a
much higher part count, because a lot of external support was needed to talk
to anything. Today we have the "system on a chip", with lots of onboard
peripherals, but a Z80 is just a CPU.

The predecessor to the "system on a chip" was the semi-custom "junk chip",
which contained unrelated stuff the standard chips didn't have. He may be
using some of those to get the parts count down. Can't tell; schematic too
small.

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TheOtherHobbes
One of the features of the Z80 was built-in memory refresh, so it needed a lot
less glue logic than most processors, which had to have external registers and
latches to handle the refresh cycles.

Way back I used to hand solder Z80 embedded controller board prototypes, and
they never needed much in the way of chippery.

In an S100 system the biggest extras were the video (formerly VDU) cards, and
the memory cards.

Both were limited by the RAM of the day, because RAM came in tiny sizes like 1
bit x 16k dynamic or 2k x 8 static. So you needed a lot of chips on a separate
board for what was really not much RAM at all.

Also, money. 64k boards cost over $1000, which is > $3k in modern money.

Now you can get 8 bit x 256k static RAM on a single chip, so you can park that
next to the processor without a separate card. With a bit of glue you can even
share it with the graphics hardware, eliminating any need for separate
graphics RAM.

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Retr0spectrum
From the title, I assumed "from scratch" meant logic gate, or even transistor
level. It's still very cool though.

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bottled_poe
Why stop there? From scratch should involve extracting the materials from the
Earth.

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Dylan16807
Because that's the point where you take things that don't compute, and make
something that computes.

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tmptmp
>>Because that's the point where you take things that don't compute, and make
something that computes.

Good point but I didn't get it quite right. What is your definition of "things
that compute"? I am curious.

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Dylan16807
A device that can use a mathematical process to figure something out.

A single transistor definitely doesn't compute. A single gate? Eh, not really.

A design with a couple latches and an adder that can perform SUBLEQ? Yeah that
computes if you attach a ram.

A non-turing-complete pipeline of math functions? Yes, that computes, though
why make that when it takes more gates than a microprocessor needs.

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awt
I am currently building my own Z80 based computer. It's been a great
experience building up my electronics lab and I wish I had done it years ago.
I recently received a Russian made Z80 that I ordered off ebay. Probably the
only product of Russia I've ever owned.

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rietta
Don't know why, but the CatChurn game jumped out at me as being written by
Yahoo Software in 1982 (the year I was born). There does not seem to be a
Wikipedia entry for this company, but the address appears to be a residential
condo as per Google Maps -
[https://www.google.com/maps/place/10970+Ashton+Ave,+Los+Ange...](https://www.google.com/maps/place/10970+Ashton+Ave,+Los+Angeles,+CA+90024/@34.0574147,-118.4461462,18z/data=!4m5!3m4!1s0x80c2bb7ddefe82d1:0xb69d54b9167a2522!8m2!3d34.056877!4d-118.445713).

Interesting to see a little bit of history and how game writers really were
working from home on an idea even in the early days.

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asimuvPR
Specially like the wooden case and keyboard. Wish the schematics were a bit
easier to read, though. :)

