PowerBook: Don‘t Make Direct Calls to Serial Chip 2/92

We're using a PowerBook 170 with software we developed. This software accesses a serial device attached to the external serial port.

When we use the same software under System 7.0.1 on a Macintosh IIci, it works fine. When we attempt to use it on a PowerBook 170, the program bombs out and the serial ports lock up. The internal modem on the PowerBook 170 doesn't appear to be interfering. All settings seem correct.

What could be the source of this problem? Were there any changes to the serial port on the PowerBook 170 that might require some sort of special serial switch?

It sounds like the application is making serial communication calls directly to the PowerBook 170's serial chip. An application should use normal communications calls to talk to the serial driver; it should never attempt to get direct access to the SCC hardware.

The serial chip is turned off when not in use (in order to conserve power). If your application makes normal serial communications calls, the serial driver knows how to turn the serial chip back on. However, an application that attempts to go directly to the serial chip will wind up talking to the chip when it's turned off, resulting in a loss of communication.

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Published Date: Feb 18, 2012