"If" a BT 16.4 switcher appears to be functional (can control through Maestro, can recieve relays), but will not perform Douts (confirmed by no functionality to switcher, or testing at back of switcher for voltage of Pulse or Latch), it is possible that FIFO needs to be disabled on the physical comport being used. Right Click My Computer and choose "Manage". Go to Device Manager/Ports (Com & LPT). Modify the comport to which the switcher is physically connected. Go to Port Settings/Advanced and uncheck FIFO. This was found to be a problem when "sharing" a switcher across a network from another machine. Has not been noted when switcher connected to machine actually performing the Pulse or Latch function.