Path: utzoo!attcan!uunet!jarthur!usc!apple!stevec
From: stevec@Apple.COM (Steve Christensen)
Newsgroups: comp.sys.mac.programmer
Subject: Re: What's the differance between serial Port A & Port B?
Message-ID: <11118@goofy.Apple.COM>
Date: 5 Nov 90 22:16:54 GMT
References: <57715.272d5199@pttrnl.nl>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 31

In article <57715.272d5199@pttrnl.nl> nugteren@pttrnl.nl writes:
>I have written a serial port driver which works fine on port A (modem port),
>but when I tried rewriting it to port B (printer port) I get error -98
>(portNotCf : Driver Open error, port not configured for this connection).
>I look in the Inside MacIntosh and I found the comment (II-246) :
>
>"The printer port SHOULD be used for output only connections to devices such as
>printers, OR at low baud rates (300 baud or less).The modem port has no such
>restrictions...."

The -98 error means that the port was configured for something else.  The
"something else" is most likely LocalTalk.  In order to use the port, you'd
have to turn off LocalTalk in the Chooser.

The only real difference between the modem and printer ports is how well they
work at higher baud rates when other things (like floppy disk use) are going
on that disable interrupts for [relatively] long periods of time.  The floppy
disk driver, for example, stashes any bytes received by the modem port while
it's reading and writing since it can't be interrupted during this time.  When
it finishes the read or write, it passes the data to the serial driver to
process as if it had received them itself...

steve

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