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From: edwatkeys@pro-sol.cts.com (Ed Watkeys)
Newsgroups: comp.sys.apple2
Subject: Re: //c serial ports.
Message-ID: <8214@crash.cts.com>
Date: 27 Mar 91 11:16:05 GMT
Sender: root@crash.cts.com
Lines: 35

In-Reply-To: message from pgc@csadfa.cs.adfa.oz.au

I'm not sure about this stuff, so if anyone corrects me, trust them...

There are a few issues that we're dealing with at the same time.  First of
all, when APple first put out the IIc, there was a timing problem with the
serial ports (they used the system clock and divided it down, to the
correct frequency, but it wasn't totallt 'correct',, if I recall).  What it
caused was data errors at speeds of 1200 ps and higher.  The solution, go
to your Apple dealer and ask him to check the serial number, and replace
the motherboard (for free, really) if it is old enough.  I had to have one
of my IIcs upgraded, and it had a sn of D4B0105.

OK, now BASIC...  at 2400bps, there could be a character coming every
4.17E-3 seconds, which means, basically, faster than BASI can handle.  Note
that GETLN is written in ML, and can handle stuff at a pretty fast rate.  I
think the problem could come when you get sent a string, a CR and then
another string.  It will take the first string okay (provided that you're
waiting for it), get the CR, and go to the next BASIC statement.  While
BASIC is picking its nose, the next line of characters is screaming by. 
For BBSs, this is not a problem, because most of us aren't *that* fast as
typers.  The only solution (the simplest) is to write the ML routines.  You
could get into interrupts and all that, but between you and I, Apple never
really told us how to use serial interrupts with ProDOS (they did in the
IIc Tech Ref, but there are a few fatal typos, and it didn't deal with
ProDOS...)  One other possibility is to talk to MDAVIS at the site where I
am, and ask him about ModemWorks.  Tell him what you need, and what you
don't, and the fact that you have a IIc, and he'll tell you if ModemWorks
will do the job for you...

Edwin Howell Watkeys III

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