The UA1 monitor read out

The trigger electronics for the UA1 proton-antiproton experiment at CERN are large and complex. A trigger monitor, containing 640 registers, is used to take a 'snapshot' of the total state of the trigger as it processes an event. The monitor's dead time is reduced by quickly reading the content of its registers into buffer memory located in both CAMAC and Remus systems. The CAMAC-computer system emulates the trigger's calculations and is used to sample and check if the trigger is working correctly. The Remus system is used for the recording of good-event data and to this end reads in the state of the trigger as a small part of this data. The readout of the 640 registers into memory, followed by the readout of memory into CAMAC and REMUS systems, is largely organised by a MC6800 microprocessor. The task is simple but achieving sufficient speed is not. Speed is achieved by minimising the number of microprocessor instructions, e.g. data does not pass through the CPU of its memory and program counting loops are replaced by either hardware counters or the stored repetition of the required number of instructions. (0 refs).