MITS 2SIO serial chip?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Fri Dec 14 19:06:02 2001

<snip>
> Dart is Z80 bus, (like an Async only SIO) not Intel. Have to take your
> word on the TCM78808 - sure it was available in 1981?
>
My old TI datasheets are hiding, so I can't verify what was when.

I'm not sure exactly what difference it makes whose bus the serial I/O chip is
designed for when the whole bunch of devices use essentially the same signals to
get the job done. The DART doesn't work much differently than any other serial
I/O device so long as you don't attempt to use some of its unique features. It
seems to me that it takes about the same quantity of machinations to make the
8250, which is also not ideally suited to the ISA bus, work on the ISA bus, as
it would take to make a Z80 DART or an 8251 or a 2651 do the job. Likewise for
the 2681/68681. No matter what you need, a small PAL will do the trick. That
certainly wasn't lost on I/O board makers.
>
I checked the actual board, and the PLCC part that I designed in to the board I
was thinking about. It turns out the early version used a few 68-pin PLCC
sockets, and, in fact, there were no 44-pin PLCC's on that board. The part in
the PLCC socket, BTW was not a PLCC, but a JEDEC 'C' package. Though there was
paper for the PLCC, the only parts used on the prototype board in that
application were in the JEDEC 'C' package. Fortunately, unlike the JEDEC 'A'
package, (that leadless single-sided ceramic chip carrier in which i80186's and
i80286's were commonly used) the 'C' package would easily work in a PLCC socket.
A later version, however, did, indeed have the 8250's in the PLCC-44 on it.
>
I really don't think practical considerations such as cost entered into the
early decision stream in the PC development, once it reached the point at which
upper management was prepared to pull the plug if at least one milestone wasn't
met. The way I heard the story from some of the guys who worked at Boca was
that there wouldn't have been an IBM PC if Intel hadn't presented the guys with
a board-level prototype of the '188 (not an application of the '188). While
it's easy enough to believe that the entire project had deteriorated into a
"Chinese fire drill," I can't believe that Intel would have had the brains to
present a canned solution to them in time to pull the chestnuts from the fire.

Dick

> > > > ----- Original Message -----
> > > > From: "Peter C. Wallace" <pcw_at_mesanet.com>
> > > > To: <classiccmp_at_classiccmp.org>
> > > > Sent: Friday, December 14, 2001 12:28 PM
> > > > Subject: Re: MITS 2SIO serial chip?
> > > >
> > > >
> > > > > On Fri, 14 Dec 2001, Gene Buckle wrote:
> > > > >
> > > > > > > NS* did use them as did many others. The worst chip was
> > > > > > > the 8250.
> > > > > >
> > > > > > Which makes me wonder what possessed IBM to pick it for the PC.
> > > > > >
> > > > > > g.
> > > > >
> > > > > The same reason they chose active high edge triggered interrupts on
the
> > > > > bus (wrong on both counts)
> > > > >
> > > > > The same reason they used 8 bits of an 8255 to read the KB shift
register
> > > > > that had a (unused) tri-state
> > > > >
> > > > > The PC = A horrible, amateurishly designed kluge
> > > > >
> > > > >
> > > > > Peter Wallace
> > > > >
> > > > >
> > > >
> > > >
> > >
> > > Peter Wallace
> > > Mesa Electronics
> > >
> > >
> >
> >
>
> Peter Wallace
> Mesa Electronics
>
>
Received on Fri Dec 14 2001 - 19:06:02 GMT