link 18 and the i o modules 16 in its rack 22 by monitoring the link 18 and looking for data 34 frames 34 containing its address for a description of the circuitry and operation of the adapter modules reference is made to schultz et al u s pat no 4 413 319 entitled 34 programmable controller for executing block transfer with remote i o interface racks 34 and issued nov 1 1983 as mentioned the remote serial link 18 may also connect to one or more nodes 26 via node adapters 24 the node adapter 24 functions analogously to the adapter 20 for the remote i o racks 22 that is the node adapter 24 provides an interface between the remote i o serial link 18 and its node circuitry 28 by monitoring the remote i o serial link 18 and looking for data 34 frames 34 containing its address the primary functional difference between the remote i o racks 22 and the i o nodes 26 is that the nodes 26 perform only a single i o function the protocol for the transmission of serial data on the remote serial link 18 is modelled after the ibm synchronous data link control 34 sdlc 34 protocol familiar to those skilled in the.