On page 3 of the Modem 300/1200 User's Manual, "Part II: Guide to Apple II",
you're told to set SW2-2 on the Super Serial Card (SSC) to the OFF position.
This isn't entirely correct.
Setting the switches this way causes the SSC to send data in 7 data bits and 1
stop bit, whereas Apple modems are only equipped to handle data in 8 data bits
and 1 stop bit. This situation causes no problems if you're using Access II or
AppleTerm. These terminal programs override the switch settings on the SSC,
and send data to the modem in 8 data b; and 1 stop bit no matter what the
switches on the SSC are set to.
It DOES cause problems, though, if you're using BASIC with your modem, since
BASIC has no such override capability. When you use BASIC with your Apple
modem, the switches on the Super Serial Card must be:
SW2-1 ON
SW2-2 ON