15 Dec
2001
15 Dec
'01
6:20 p.m.
That's what clocks are for. As I wrote before, you derive the /IORQ from the
/IOR and /IOW, build your select from those as well, and then use a registered
output for the /RD signal. The default bus clock is 8 MHz, and the default for
the -A SIO/DART is 4. That should provide enough setup time.
Dick
----- Original Message -----
From: "Peter C. Wallace" <pcw(a)mesanet.com>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, December 15, 2001 10:33 AM
Subject: Re: MITS 2SIO serial chip?
Well ... we digress ... I never liked the Z-80 setup because the peripherals
basically limited the CPU speed, and I liked the Z8000 series even less, though
I don't remember why. I didn't EVER use an Intel product (other than at the
board level) until the 80186 came out, BTW.
On Sat, 15 Dec 2001, Richard Erlacher wrote:
for
Well, that doesn't change the fact that if
you AND /IOR with /IOW you get a
useable /IORQ. Whether you feed the /IOW forward doesn't matter.
Except that you need to have a valid read signal before IORQ...
>
> I stand corrected on my presumption that the M1 and IORQ were used solely > the int handshake. I never liked the Z80
peripherals and never even once
used
> one in my own work, though they were everywher in
commercial hardware. Even
my
HP plotter has
one it it, though it doesn't have a Z80.
Actually I thought the Z80 peripherals were quite nicely
integrated with the Z80, with the status affects interrupt stuff, daisy
chained interrupts and other nice ideas. (many of which had been done
before in minicomputers) They also had consistant reset polarity's and
basically look like they gave a lot of thought to System Design, not just
chip design. When we moved from designing Z80 stuff to embedded PC stuff
it was like going back to the stone ages. The Intel stuff being a rag-tag
pile of ****
The Z8000 stuff was even nicer, with Multiplexed data/address bus
so the all peripherals could have 256 directly addressed registers without
losing valuable pins on the 40 pin chips...
>
<snip>
>
> > Dick
>
> > ----- Original Message -----
> > From: "Peter C. Wallace" <pcw(a)mesanet.com>
> > To: <classiccmp(a)classiccmp.org>
> > Sent: Saturday, December 15, 2001 8:38 AM
> > Subject: Re: MITS 2SIO serial chip?
>
>
> > > On Fri, 14 Dec 2001, Richard Erlacher wrote:
> >
> > > > I don't think the
DART would have been such a mess. If you AND (/IOR
and
> /IOW)
> > > you get a useable IORQ, not that you really need it, since it's only
used in
> > > conjunction with M1 to signal the
mode-2 interrupt acknowledge, which
> wouldn't
> > > occur in this case. If the device is selected I'm not at all sure it
cares
> > one
> > > > iota whether IORQ is active.
> >
> > > Not true, the DART like the
SIO has no write signal...
> >
> >
>
> > > > see below, plz.
> > >
> > >
> Dick
> > > > ----- Original Message -----
> > > > From: "Peter C. Wallace" <pcw(a)mesanet.com>
> > > > To: <classiccmp(a)classiccmp.org>
> > > > Sent: Friday, December 14, 2001 6:45 PM
> > > > Subject: Re: MITS 2SIO serial chip?
> > >
> > >
> > > > > On Fri, 14 Dec
2001, Richard Erlacher wrote:
> > > >
> > >
> > > <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.
> > > >
> > >
>
> > > > > The 8250 is a
direct ISA bus interface (no logic other than decode
needed)
> > > > The DART would be a mess, using
the Z80s M1,IORQ and all that. (not
that
> > > > > there's anything wrong with the Z80 way)
> > > >
> > >
> Not exactly direct. you do have to invert the ALE to form the
DataStrobe or
> > > whatever that signal was. I always
liked the 8250 because it was a
1-part
> > > solution to a problem otherwise using
two or more parts. It is a
convenient
> > > part for the ISA, but since the ISA
presents all the other signals,
/IOR,
> /IOW,
> > > etc, from which you can derive the required signals in a 16L8 anyway,
which
> is
> > > what most of them used for decoding the addresses, you could make
whatever
> > > > signals you needed.
> >
> > > Yes exactly direct! There is
only decode and direct connection from IOW to
> > > input data strobe and IOR to ouput data strobe. Take a look at the Asyc
> > > card schematic in the XT tech ref. ALE is not needed for I/O on the ISA
> > > bus, only for latching the LA bus (which is above the 64K limit of I/O).
> >
>
>
> >
> > >
> > >
> > >
> > > 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.
> > > >
> > >
> > Sure, there are 8250's (and 16450's and 16550's etc etc) in PLCCs,
just
> > > > > not in 1981...
> > > >
> > >
> > >
> > >
> > > 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(a)mesanet.com>
> > > > > > > > > > To: <classiccmp(a)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
> > > > > >
> > >
> > >
> > >
> >
> > > > >
> > > >
> > > > > Peter Wallace
> > > > > Mesa Electronics
> > > >
> > >
>
> >
>
> > >
> >
> > > Peter Wallace
> > > Mesa Electronics
> >
>
>
>
>
>
> Peter Wallace
> Mesa Electronics
>
>