[vcf-midatlantic] First homebrew computer project

[Joseph Giliberti]

Hi John,

My current inventory of MCS-80 components:
C8080A CPU (gold/white)
P8212 8-bit I/O port
C8214 priority interrupt control (gold/white)
(2) D8216 4-bit bi-directional bus driver
D8228 system controller & bus driver
(2) D8238 system controller & bus driver
C8255 programmable peripheral interface (gold/white)
(3) C2112A 256x1 bit SRAM (gold/white)

I'm sure I'm probably missing one or two crucial support chips. I'll
definitely need a bunch of a much higher capacity RAM, since 96 bytes just
doesn't seem like enough. I'm pretty sure I have a ton of SRAM chips of
more reasonable capacity but I just have to dig them out. Same goes for
EPROMS

As as far as construction and form factor, I was thinking about doing it on
s100 prototype boards and a large backplane so that I could add
commercially built cards to the system. I might eventually want to add a
floppy controller. I know it would probably make more sense to use some
type of flash interface, but I want this machine to be configured as if it
was built in the late seventies or early eighties.

Thanks,
Joe Giliberti

On Sat, Jan 1, 2022, 7:11 PM Jonathan Chapman via vcf-midatlantic <
vcf-midatlantic at lists.vcfed.org> wrote:

> 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
>