Readout sequence control

A timing signal for a readout sequence is handled by a central sequence controller and TDMs. The sequence controller receives a timing signal from the trigger system and distributes it to TDM located at the VME crate of each detector readout system. The handshake sequence is simply accomplished with the level of a single busy line from TDM to the sequence controller. Upon receiving a trigger signal, TDM generates an interrupt or raise a data ready flag to start a readout sequence. The busy line has to be raised and reset either by an external signal or by setting an internal register to receive the next trigger. The length of the deadtime after resetting the busy line is programmable, in order to compensate the cable delay between the readout crate and the front end electronics. If no busy lines from the TDM modules are raised, the sequence controller initiates a readout sequence by a timing signal received from the trigger system. The trigger related information, such as trigger rates, deadtimes, and the beam bunch number, is monitored. In addition, the response time of the busy line from each sub-detector TDM is separately monitored, so that the location of a problem can be easily identified. The system is driven by 16/64 MHz clock pulses derived from the accelerator RF, and 16 MHz clock pulses are also distributed to TDM.