Serial-bus based trigger timing distribution system

We have developed a serial-bus based trigger timing distribution system to handle the trigger and related timing signals over more than one thousand newly developed pipeline data acquisition modules for the Belle detector at the KEKB storage ring and for the SuperKEKB upgrade. The main idea is the use of 10-bit serial-bus lines over an inexpensive, compact and widely available enhanced category-5 shielded twist pair (STP) copper cable. The serial-bus is operated at 42.33 MHz, resulting in a 508 Mbps serial data transfer over the STP cable up to a distance of 15 m. The entire system consists of only three types of modules. The system is highly scalable by cascading switch modules over multiple stages: we use 4 stages to handle up to 4096 readout modules. We have proved that the basic technology is suitable for such an application. A two-step integration procedure before the full replacement is planned to integrate the system into the running Belle data acquisition system.