Re: A multiport serial board would be nice...

[dempson@actrix.gen.nz (David Empson)]

In article <368hao$70n@zircon.cs.uow.edu.au>,
David E A Wilson <david@zircon.cs.uow.edu.au> wrote:
> dempson@actrix.gen.nz (David Empson) writes:
> 
> The mail I have received so far indicates that people would like to
> be able to use existing telecom programs (at least on the first port).
> 
> Unfortunately this means that I would be unable to use any of the
> newer serial chips (I am getting info on the Signetics SC26C94 Quad
> UART and SCC2698B Octal UART chips) as I believe that all comms
> programs talk directly to the hardware rather than just using the
> Pascal 1.1 interface (as it has no support for interrupts [or at
> least no cards have implemented it] - correct?). 

It depends on the card.  The Super Serial Card firmware doesn't support
interrupts, so all comms programs that require a SSC go directly to
the hardware.

The IIgs serial firmware _does_ support interrupts.  Software that
uses the IIgs serial ports are supposed to use the firmware.

I can't see why anyone would want to use existing comms software.  The
whole point of a multi-port serial card is to support a multi-user
BBS, surely?  I can't see any other use for it other than a lazy way of
selecting one of several different connections (which could be done
with an external switch box).

Assuming the card didn't use the 6551, there is also the benefit of
having flow control lines that don't interfere with data transmission
and reception.

The only other benefit I can see might be high-speed communication
(assuming you used a more powerful serial chip).  Either of the last
two items would require rewriting part of the comms program (or
writing a custom driver, if possible).

> Even worse would be if I go with the suggestion that the card have an
> onboard CPU to lessen the interrupt load on the //. There is no way
> that this interface would look like any serial chip known to man...

It sounds like you've run into the same problems that I did.  I
proposed making a new serial card a few months ago.  I was thinking of
using a dual 16550-based chip, but it turned out I couldn't source
them in New Zealand.  There didn't really seem much point making the
card as there would be no software to use it.  It also wouldn't have
been powerful enough for some applications.  A design with an onboard
CPU, buffering memory and possibly DMA support would be much more
flexible (but more expensive). 

> I suppose I could add a 65c51 chip as port 0 for backwards compatibility.

I suppose so.  Yuck.  That means you have to put the 6551 at $C0x8 to
$C0xB, making a nice hole in the middle of your DEVSEL I/O space.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand