Path: utzoo!attcan!uunet!mcsun!hp4nl!dnlunx!dnlts!nugteren
From: nugteren@pttrnl.nl
Newsgroups: comp.sys.mac.programmer
Subject: What's the differance between serial Port A & Port B?
Message-ID: <57715.272d5199@pttrnl.nl>
Date: 30 Oct 90 09:10:32 GMT
Organization: PTT Research Neher Laboratories, The Netherlands
Lines: 24

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...."

I also found this remark (III-24) :

"Port A and Port B are identical except that Port A (the modem port) has a
higher interrupt priority, making it MORE suitable for high-speed
communication"

What should I make from this? Does it mean I should be able to configure port B
for 1200 baud input at my own risk of hardware overrun errors, or is such a
configuration internally restricted? I get the feeling the former is true,
because when I try to configure port B for 300 baud I get the same error.
What's going on? It's got to be a bug in my code but I can't find it anywhere.

I hope someone out there can help,

Nils