Re: Question: Multiple Super Serial Card ][s in //e?

[pausch@saaf.se (Paul Schlyter)]

In article <991cmh$8e4$1@acme.gcfn.org>,
Dave Althoff Jr <dalloff@gcfn.org> wrote:
 
> You can put SEVEN Super Serial Cards in your //e if you want.  Don't know
> why you'd want to do that since that would prevent you from having a disk
> drive or a 80-column board,
 
OTOH you could connect an 80-column serial terminal to the Super Serial
Card in slot 3 -- that would give you an 80-column screen.....
 
> but you can do it.  None of that messy IRQ interference stuff that you
> run into on the Wintel machines.....!
 
OTOH interrupt-driven I/O has a lot of advantages: type-ahead
buffers, serial port buffers, etc etc.  It's very easy to lose a
character on the Apple, and implementing a file transfer protocol
like Bimodem (which attempts to utilize the full bandwidth of the
phone connection by transferring files in both directions
simultaneously -- in that way you could swap files with your friends
in half the connect time) would be impossible.
 
But you could on Wintel machines switch off the interrupt signals
from the I/O cards, and get rid of IRQ problems in that way.  Then
you'd of course have to rewrite the software drivers for that card
from interrupt-driven mode to polled mode .......  after running
these drivers for awhile you'd probably want very much to go back to
interrupt-driven mode....
 
Finally: isn't it possible to turn on an interrupt signal on the
Super Serial Card?  Now try to do that on more than one of those
seven SSC's, and you'll immediately run into a severe problem: the
Apple II only has one IRQ line, not 8 or 16 as the Wintel machines
have....
 
-- 
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