In order to use your Sportster modem on a Macintosh, you will have to put DIP
switches 1, 3, 5, 7 and 8 in the DOWN (ON) position.  If you require
auto-answer, then leave DIP switch 5 in the UP (OFF) position.    Also, there
is another item which requires attention other than the modem configuration.
There are two cables that are available for the Macintosh.  The first is the
more common, which is a standard serial cable.  The second is called a
'hardware handshaking' cable, which provides the CTS/RTS signals necessary for
hardware flow control.  The modem may be failing because you are trying to use
hardware handshaking with a standard serial cable.  If you make the DIP switch
changes as above, and change the initialization string to "AT&F&B1&H2&I2" (for
software handshaking), the modem will more than likely work.  If you are not
sure which kind of cable you are using, then use the software flow control
string first, and then try the hardware flow control string: "AT&F&B1&H1&R2".
If the latter does not work, then you do not have a cable that supports
hardware flow control.  The proper lights that should come on at power up are
the "CS" (should be on at all times), the "TR" (because DIP switch 1 forces
the DTR signal high), and the "AA" if you have DIP switch 5 UP (OFF).  You
should then see the "RD" and "SD" lights flickering as you type commands to
your modem.  After you have configured your modem with the proper settings,
you can put DIP switch #7 back in the UP (OFF) position.  If the last steps do
not work, then there could be a problem with either the cable or the modem.
Please try the modem with another cable before assuming that the modem is not
functioning correctly.

Thank You.

U.S. Robotics On-Line Support