Appendix
In this appendix
What is SDLC?
5
What is SDLC?
SDLC stands for Synchronous Data Link Control protocol. It was developed by IBM in the
mid-1970s as part of their Systems Network Architecture. While not used commonly in
modern computer systems, it is still found among modern trac controllers.
When TS2 controllers were introduced, the specication indicated that cabinet interfaces
were to be based on data transmission rather than discrete signals. SDLC is intended to
connect the controller, the MMU (Malfunction Management Unit—the conict monitor
in TS1 controllers), the detection system, and the terminals and facilities unit (the back
panel). is greatly reduces the complexity of signal controller cabinets and replaces the
need of hundreds of conductors required to provide discrete signals (contact closures, etc.)
throughout the cabinet.
ere are many advantages to SDLC but the most signicant is the reduction in cabinet
cost, eliminating hundreds of small wire connections and the elimination or reduction in
the size of the rack used for contact closures.
What are TS1/TS2 Controllers?
TS1 controllers were introduced in 1976 and reissued in 1983, 1989 and 1994. ey coex-
isted with TS2 until about 1999. e design of the TS1 included the function and electrical
characteristics for pins on the three connectors designated as A, B, and C. In addition they
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