There is not a hardware problem with the serial ports. The "port in use" message is the result of a software conflict between the Apple Telecom software and the printer driver.
The Apple Telecom software takes complete control of the modem port when installed on a Power Macintosh. It must do this to make applications recognize the external modem. Any data that is sent to the modem port is interpreted as data meant for a modem and is processed by the Apple Telecom software. The Apple Telecom software combined with the GeoPort adapter essentially create a softwarebased modem.
So, although you can disconnect the GeoPort Telecom Adapter and connect the printer to the modem port, the Telecom software is still installed. Because the Telecom software is still installed, it will send data out the modem port as if it was meant for the Telecom Adapter. The software expects to control the modem port whether or not an adapter is attached, and this results in the "port in use" error message or unusual printouts.
The only workaround is to de-install the Apple Telecom software using the installer application.
This article was published in the "Information Alley":
Volume II, Issue 18, Page 6
Article Change History:
26 Jan 1996 - Added Info Alley information; made minor technical updates.
05 Jan 1995 - Corrected typos.
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