Apple Power Macintosh 7300 series - PC Compatibility Card - Manual (Page 53)

IMPORTANT Mac OS programs cannot access a port that you’ve assigned to the
PC environment. If you’re trying to print, fax, or use your modem in the Mac
OS environment, and you get a warning message that the port requested is
busy or in use, then you need to unassign a PC COM port in the PC Setup
control panel.
Setting up a modem or other serial device
From the PC environment, you can use a modem or other serial device
connected to the Macintosh serial port. For best results, use the Apple DB-25
DIN-8 Mac to High-Speed Modem cable (part number M5537LL/A). If you
are unable to obtain this modem cable, you can use the information in the
next section to build a custom cable.
Because the Macintosh uses the RS-422 protocol, the RS-232 Ring Indicator
(RI), Request to Send (RTS), and Data Set Ready (DSR) signals are not
available through a Macintosh serial port. You can attempt to configure your
application to use the carrier string or ignore carrier detect.
Note: The serial port on the optional PC Serial and Parallel Port card (not
included) supports the RS-232 interface directly without your having to use a
special cable or configure your software.
Note: For more information on setting up a modem in Windows 95 to use
TCP/IP for PPP (point-to-point protocol) connections, see Appendix D,
“Installing Network Client Software.”
53 Setting Up the PC Environment