Overview of the SPS/LEP fast broadcast message timing system

A fast broadcast message system, also referred to as the general machine timing system, has recently been installed at CERN's Super Proton Synchrotron (SPS). It is used to control the SPS in its roles as a multi-cycling, multi-user service accelerator. The messages are centrally generated by an IBM compatible PC/AT card and broadcast to all users of the system. At the receiving end the frames are decoded and presented to the user in the form of either an interrupt to his intelligent equipment, a hardware pulse or a short message. They are used to synchronise the SPS when used as a 450 GeV fixed target machine, a 315 GeV p-pbar collider, a 100/450 GeV pulsing-coasting machine and also as an injector for the Large Electron Positron (LEP) machine. In the future it will also be used for LEP control. Implementation details and constraints are described, as are experience to date and foreseen expansions