Serial digital interfaces

The serial digital interfaces are used to exchange digital data words between core and peripheral elements. The interface timing and clocking signals are controlled by the core element. A serial digital interface which reads data from the peripheral element into the core element is called an input serial digital (ISD) interface. A serial digital interface which writes data out from the core element to the peripheral element is called an output serial digital (OSD) interface. A third class of serial digital interface is also introduced in this standard, namely the bi‐directional serial digital (BSD) interface.

For space applications, serial digital interfaces shall be implemented in balanced differential form. In this form each signal is carried by a pair of conductors and the level of the signal is determined by the differential voltage between those conductors.