This will result in unacceptable noise in your signal or a complete failure in the two devices to interpret the transmitted voltage levels correctly. Serial communications using RS-232 voltage levels depend on reference to ground. This is a common cause of your program getting stuck in the vSyncWait routine as the serial driver is waiting for character transmission to complete while the SCC waits for an appropriate DTR or CTS that can't be seen due to a lack of proper ground reference. PowerBook modem has been designed with a minor deviation from the Hayes modem command set standard. The Hayes command set deviation is documented on page 88 of the FaxModem user's guide.
Many programs begin their modem initialization by issuing a modem break command.
The Power Adapter port on the PowerBook has been engineered with a mechanical switch that detects the presence of the adapter. Software detects the insertion of the plug into the PowerBook Power Adapter port, and, during the attempt to charge the battery, the lightning bolt icon that appears in the Battery desk accessory toggles on to indicate that the charging apparatus is attempting to bulk charge the battery. In the status byte returned by BatteryStatus, bit 0 indicates the presence of the physical plug in the power connector. Bit 1 indicates if the charging circuit is set to bulk rate or trickle. There is no way to determine if the attached charging apparatus is providing current, as the circuit can read only the voltage level of the entire system.