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).
The 8250 was a fine chip for the application, though I wonder why they used the
DIP version. 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.
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
>
>
Received on Fri Dec 14 2001 - 14:24:12 GMT