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From: merlyn@digibd.com (Brian Westley (Merlyn LeRoy))
Newsgroups: comp.sys.mac.comm
Subject: Re: A question for the hardware wizards at Apple
Message-ID: <1990Nov26.024613.22610@digibd.com>
Date: 26 Nov 90 02:46:13 GMT
References: <G1|^CJ$@ads.com>
Organization: DigiBoard Incorporated, St. Louis Park, MN
Lines: 22

jtn@ADS.COM (John T. Nelson) writes:
>.. Someone on the net
>mentioned that the problem with high speed communications and the Mac
>is that there just aren't enough control lines... i.e. you cannot use
>hardware flow control on the Mac serial ports.  This seems unlikely
>since Apple does provide lines "Handshake In and Handshake Out" on the
>serial port, although the exact meaning of these names is quite vague.

The Mac serial ports supply exactly one hardware input and one hardware
output, "CTS" and "DTR", repectively.  The hardware input line, "CTS",
is variously used as CTS (hardware flow control), DCD (carrier detect
when connected to a modem), or external clock.  If your software package
insists that "CTS" be used as carrier detect and won't allow you to use
it for hardware flow control, you can't use it for hardware flow control.
If you use "CTS" for hardware flow control, it's going to be difficult to
determine the state of carrier detect (but chatty modems can help).
You can use it for one thing at a time; you can't use it for two different
things simultaneously, like CTS & DCD.

----
Brian Westley
DigiBoard