S-LINK, a data link interface specification for the LHC era

In the Technical Proposals for the ATLAS, CMS and ALICE experiments at CERN, there is a requirement for several thousand data links. Although there is an obvious need for standardisation, this seems difficult to achieve as the links run at different speeds, over different distances and have various constraints of power consumption, size and radiation hardness. An additional complication is that today one cannot decide which will be the most cost effective technology for the implementation of the final links. Furthermore, one must allow designers of boards at each end of the link, for example read-out electronics and input buffers, to work in parallel with the development of the links. The S-LINK is a new concept which should provide the benefits of standardisation without these limitations. The S-LINK specification defines, at both ends of the link, a simple FIFO-like user interface which remains independent of the technology used to implement the physical link. The physical link provides transfer of event data and control words, error detection, optional flow control and test facilities. The paper describes the S-LINK specification and gives examples of the use of the S-LINK, the physical links being designed, and the test equipment that is being developed.