Due to the RS-232 implementation of the Macintosh, not all RS-232 signals are
available. These signals are not available: Carrier Detect (CD), Data Set
Ready (DSR), Request to Send (RTS), and Ring Indicator (RI). If your
application or serial device requires these signals, it will not work.
The DOS Compatibility Card does not support Carrier Detect (CD). You must
configure your communications applications so they do not use CD. Most
communications applications can be set to respond to the CARRIER string sent
back by most modems.
The work around is for the customer to configure their software to use XON/XOFF
for flow control. If their software does not allow for XON/XOFF then the
software will not run on our DOS Card.
The serial problem is the same for all Macintosh computers, but SoftWindows does some special software processing of serial signals to "emulate" the missing RS-232 signals. The SoftWindows manual has the following information:
Serial Limitations-
Programs that do not work well are those that are extremely timing sensitive, or that rely on serial port lines that are not available on the Macintosh serial port.
SoftWindows has no access to the DSR, DCD or RI signals, and the RTS line cannot be set up, due to lack of lines. Instead, SoftWindows makes the DSR and RLSD/DCD lines seem to always have the same status as the DTR line. RI is always set to off.
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