MITS 2SIO serial chip?

From: Peter C. Wallace <pcw_at_mesanet.com>
Date: Fri Dec 14 17:47:46 2001

On Fri, 14 Dec 2001, Richard Erlacher wrote:

>
> ----- Original Message -----
> From: "Peter C. Wallace" <pcw_at_mesanet.com>
> To: <classiccmp_at_classiccmp.org>
> Sent: Friday, December 14, 2001 2:19 PM
> Subject: Re: MITS 2SIO serial chip?
>
>
> > On Fri, 14 Dec 2001, Richard Erlacher wrote:
> >
> > > Horsefeathers! The reason they did all the stupid stuff they (IBM) did was
> > > because INTEL told them to, since there was nobody on the PC team smart
> enough
> > > to design a microcomputer, yet dumb enough to risk doing it in their (IBM's)
> > > corporate environment. ISTR that the original cause for the presence of the
> > > 8255 was the need for it in the parallel port (see the comments in the
> original
> > > BIOS listings in the tech ref).
> >
> > Fishfeathers! I stand by my original post. whether Intel helped create the
> > mess or not is immaterial...
> >
> Nobody, including the dumbest at IBM, was dumb enough to use the high-level,
> positive edge-triggered interrupt without pressure from Intel. Apparently Intel
> had ONE guy at some time in history who devised that ridiculously stupid
> approach to interrupt processing and built it into their "scheme" which was
> followed by a series of devices that lived on that scheme. Once they had it,
> they were stuck with it.
> >
> > > The 8250 was a fine chip for the application, though I wonder why they used
> the
> > > DIP version.
> >
> > What other 8250 option than 40 pin DIP was available in 1981?
> >
> PLCC-44

The 8250 was not available in PLCC at that time... I have WD and National
data books of that vintage and no PLCC44 8250s...


> >
> > There were better choices available, but they didn't want to lose
> > > the serial port board business by putting two of them on the same card, and
> by
> > > that time serial I/O chips tended to have between 2 and 8 ports on them.
> >
> > Nonsense, What 8 port chips were available in 1981? Were there even any
> > 2 port chips for the Intel bus?
> >
> dual: Signetics 2681/68681, Z80 DART would have worked fine too, with the
> exception that the Intel bus didn't work with the "mode-2" interrupt, which you
> weren't require to use; octal: TCM78808 which looked pretty much like 8 2661's.
> I didn't like the package.
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?



> > >
> > > 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 - 17:47:46 GMT