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_at_mesanet.com>
To: <classiccmp_at_classiccmp.org>
Sent: Saturday, December 15, 2001 10:33 AM
Subject: Re: MITS 2SIO serial chip?
> On Sat, 15 Dec 2001, Richard Erlacher wrote:
>
> > 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
for
> > 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...
>
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.
> >
<snip>
> >
> > Dick
> >
> > ----- Original Message -----
> > From: "Peter C. Wallace" <pcw_at_mesanet.com>
> > To: <classiccmp_at_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_at_mesanet.com>
> > > > To: <classiccmp_at_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_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
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > > Peter Wallace
> > > > > Mesa Electronics
> > > > >
> > > > >
> > > >
> > > >
> > >
> > > Peter Wallace
> > > Mesa Electronics
> > >
> > >
> >
> >
>
> Peter Wallace
> Mesa Electronics
>
>
Received on Sat Dec 15 2001 - 18:20:25 GMT