In a work conveying system including at least a work holder for holding a work and a horizontal mover for moving the work holder horizontally in an upper ceiling space within a clean room, the work being conveyed to each of plural processing apparatuses. A discrete event simulation of a scenario is performed via a process executing on a system. The shaft includes a conduit and a staple mechanism. When an initial link down condition is detected, the issuance of a link down signal is delayed for a predetermined period of time from the detection of the squelch voltage over the serial link.