4004/8008 (was Re: Forgotten PC History)

[Ethan Dicks]

On Mon, Aug 11, 2008 at 07:08:43AM -0700, dwight elvey wrote:
> 
> > From: ethan.dicks at usap.gov
> >>
> > Hmm... I happen to have a couple of 4004 chips (one pulled from a
> > non-UPC barcode scanner, the other from a commercial kitchen scale),
> > and I've long fantasized about building some showcase 4004 circuit,
> > probably a digital clock.
> >
> 
> Hi Ethan
>  The chip is P-mos and it doesn't directly connect to ttl.

I do remember that it is P-MOS, but that's a bit out of my
experience - I got my start in the CMOS and TTL days of the
late 1970s.  What little I know about older circuit types (RTL,
DTL, etc.) is from playing with DEC equipment.

I am not surprised to hear that it won't connect directly
to TTL, but I was thinking a 4007 or 4050 might do the trick.

> The down is very week and only pulls up with any
> strength.

OK.

>  There were a couple chip interfaces ( 4008 and 4009 )
> that created TTL level signals to run standard RAM/ROM.
> The only issue here is that one lost the instruction stream
> so that one couldn' t take advantage of any RAM ot ROM
> specific commands.
>  The later came out with a single chip version of the
> interface( I think it was 4269 ).
>  These come up on ebay every now and then.

OK.  I don't know if I have _those_ exact chips, but I do
have some support chips along with the processors.

> The manual on Al's site shows a circuit to convert the Pmos
> levels to a TTL eprom ( used on the SIM4-1 ). The circuit does
> use 4002-1 and 4002-2 RAMs.

Those I have, at least one or two of.

The EPROM interface sounds quite useful - that was really my
worry since it's not possible to order genine MCS4-family
ROMs anymore.

>  The 4001/4002 had built in I/O. They would watch the instuction
> steam and execute an I/O operation when the 4004 executed
> the fetched instruction.

Right... I remember something about built-in I/O ports, but not
the details.

>  It is easier to modify a -12V supply to power the -10v than
> to make a converter. Many floppy disk supplies are fine for
> this.

Sure.  I was just hoping to be able to dedicate a square inch or
two of the design and have a single-supply board.  I also have
some +5V/-12V potted chargepump blocks at home, a remnant of
a particular COMBOARD design for a DEC chassis that lacked -12V
or -15V to run the EIA level shifters.  Those might be able to
put out more than a few mA at -12V.

Thanks for the more detailed info,

-ethan

-- 
Ethan Dicks, A-333-S     Current South Pole Weather at 11-Aug-2008 at 19:40 Z
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Ethan.Dicks at usap.gov            http://penguincentral.com/penguincentral.html