The KeyLargo IC has a traditional Macintosh serial port that is connected to the modem slot. The KeyLargo IC also provides digital audio to the slot in the form of an I2S port that shares pins with the serial port.
The KeyLargo IC provides DB-DMA (descriptor-based direct memory access) support for the modem slot interface.
The internal hardware modem is a separate module that contains a modem controller IC, a datapump, and the interface to the telephone line (DAA). For more information about the modem, see Internal Modem .