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From: shawn@marilyn.UUCP (Shawn P. Stanley)
Newsgroups: comp.sys.apple2
Subject: Re: Apple can't keep up with 2400 baud
Message-ID: <57@marilyn.UUCP>
Date: 10 Jul 90 22:38:32 GMT
References: <9228.apple.net.info-apple@pro-harvest>
Reply-To: shawn@marilyn.UUCP (Shawn P. Stanley)
Organization: Litfal
Lines: 23

In article <9228.apple.net.info-apple@pro-harvest> crew@pro-harvest.cts.com (Chris Wicklein) writes:
>In-Reply-To: message from GRAY@ADMIN.HumberC.ON.CA
>   Unless I read you wrong, you're saying -NO- Apple II can run an 80-col.
>display @ 1200 or more bps?!?!?! Do you mean that the original Apple II /
>Apple II+ can't, rather than the whole family?

Without using interrupts or polling, the 80-column display/scrolling
firmware is too slow, and during the time characters are being displayed,
other characters coming in can be lost.

The Apple IIgs has support for interrupt-driven serial I/O, and without
modifying how the display routines work, can keep up nicely.  This is also
true of an Apple II using, say, a Super Serial Card with interrupt support
in both the hardware and the software.

Polling can be accomplished by writing display routines that check for the
presence of incoming characters when performing such time-intensive tasks
as scrolling the 80-column screen, possibly after moving each line of text.
That's only 24 checks per scroll at the most, and that won't slow down
scrolling noticeably.
--
Shawn P. Stanley         shawn@marilyn.marilyn.mn.org
bungia!marilyn!shawn     {rosevax,crash}!orbit!marilyn!shawn