Hybrid communications link adapter incorporating input/output and data communications technology

There is disclosed a data communications link adapter (10) providing flow of data control and status information between an input/output (I/O) backplane (12) and a fiber optic frontplate (14). The adapter represents a melding of I/O channel extender technology and data communications technology: a dedicated processor handles linklayer protocol, leaving to software only higher protocol layers; a flow-through architecture is provided by the adapter; a combination of windowing and handshaking are used; and a relatively short frame of sixteen bytes is employed. The adapter includes a backplane adapter portion (16) which serves to interconnect host equipment, a processor portion (36) dedicated to layer 3 (circuit operations) a protocol controller (20) dedicated to layer 2 (physical layer) operations, a fiber optic interface portion dedicated to layer 1 (physical link) operations, and an arbiter portion (38,40,42) which couples the processor (36) to a data path (22) connecting the backplane adapter and the protocol controller. The arbiter (38) controls data accesses that use a portion of the data path connecting the backplane adapter (16) to the protocol controller (20) and a data path between the protocol controller and the processor (36). A variety of data integrity measures are implemented on all data paths. The adapter facilitates data flow-through by buffering internal to the protocol controller, and has extensive data flow control features.