[vcf-midatlantic] First homebrew computer project

[Jonathan Chapman]

Welcome back! If you aren't doing a S-100 compatible setup, do use the Intel 8228 system controller. It makes life *much* nicer.

If you're using MCS-80 parts anyway, the Intel 8251 or 8251A is a solid choice for your serial chip.

You will need either a power-on jump circuit (see Cromemco ZPU) or ROM relocation circuit (you're welcome to use the one from the 8085 SBC rev 3 if you like) to keep ROM from being hardwired at 0x0000, which is incompatible with CP/M.

Probably best to use modern SRAM, or at least modernish byte-wide stuff like the 62256, 6264, or 6116, just to avoid having to get a ton of old power-hungry RAM.

There are lots of ROM monitors available, I of course usually customize GWMON-80 for systems I'm bringing up:

https://github.com/glitchwrks/gwmon-80

Just restructured and cleaned up the source a month or so ago and decided to call it V1!

Thanks,
Jonathan

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Saturday, January 1st, 2022 at 14:48, Joseph Giliberti via vcf-midatlantic <vcf-midatlantic at lists.vcfed.org> wrote:

> Greetings Everyone,
>
> I'm Joe Giliberti. I had been a member of the original MARCH up until 10 or
>
> so years ago, when a personal issue prompted me to leave. It also didn't
>
> help matters that it took me more time than most to grow up into a
>
> responsible adult. Now that many things have changed and that I've been
>
> getting back into the hobby over the past few years, I've decided to come
>
> back. I keep making plans to get to events but something always seems to
>
> interfere. I'm really hoping I'll be able to get to the workshop on Sunday.
>
> Any who, in the past few years I've been getting more and more into the
>
> hobby, doing lots of reading to expand my knowledge beyond writing BASIC on
>
> my Apple IIe. I've decided that I want to take a shot at constructing a
>
> basic computer.
>
> Over the years, I've been amassing component parts from estate sales and
>
> one particularly lucky estate cleanout. Among other things, I've
>
> accumulated thousands of capacitors, resistors, transistors and diodes,
>
> hundreds of 7400 series TTL and quite a few microprocessors and support
>
> chips.
>
> I think I want to base the computer around an 8080. There are the two main
>
> reasons I want to go this route:
>
> -I have an 8080A and many of the support chips, most of which are of the
>
> early gold and white ceramic design.
>
> -Ultimately, I want the system to be capable of running CP/M
>
> Initially, I'm not looking to make it overly complicated. Ideally, I'd like
>
> to have a machine language monitor and TinyBASIC in ROM. I'd also like a
>
> serial connection for I/O and a cassette interface for mass storage. If
>
> someday I get really ambitious, I might look into things like video
>
> hardware and floppy disk mass storage, but I need to take care of the
>
> basics first
>
> I still need to do a lot more research and study before I start doing
>
> things like design and construction, but I would very much appreciate any
>
> suggestions or feedback on my plans for this endeavor.
>
> Thanks and Happy New Year!
>
> Joe Giliberti