The electrical characteristics of a serial communications connection are specified by various interfacing standards. These two signals are connected to each other. For specific information about how these signals are used in Macintosh computers, see Guide to the Macintosh Family Hardware , second edition. Asynchronous and Synchronous Communication Serial data transfers depend on accurate timing in order to differentiate bits in the data stream. The terms asynchronous and synchronous are slightly misleading because both kinds of communication require synchronization between the sender and receiver.
Asynchronous communication is the prevailing standard in the personal computer industry.
Asynchronous communication is a protocol for coordinating serial data transfers. Asynchronous execution refers to the capability of a device driver to carry out background processing. Serial endpoints support both asynchronous communication and asynchronous execution. Open Transport serial endpoints do not support synchronous communications protocols. However, they do support synchronous clocking supplied by an external device.