Design and performance of the LANL neutron science center time-of-flight/area VXI module

This paper describes the design and performance of a new VXI-based Time-of-Flight/Area Detector (TOF/A) module used at the Los Alamos National Laboratory (LANL) Manuel Lujan Neutron Scattering Center. Working in conjunction with external Area-Detector electronics developed by Brookhaven National Laboratory, the module accepts 10-bit x- and y-input data along with necessary hand shaking signals to generate 64-bit wide data events. The module uses field-programmable gate arrays (FPGAs) and differential-input RS-422 signal conditioning for a flexible topology. Two frame FIFOs, each 16 k-words deep by 64-bits wide, accumulate event data at up to 450 kEvents/sec during a frame until the host CPU can read out the data. One FIFO is read while the other is being filled. The FPGAs have been programmed to interface, control, and read data from the area-detector electronics. Each 64-bit event word consists of a 24-bit time stamp, an 8-bit channel identification number for when multiple modules are used in one VXI crate, 10 bits each for x and y position, and 12 bits which are presently undefined. Using a backplane 10-MHz clock, timing resolution is ±50 ns. The paper describes the block diagram of the module including a description of the timing, data and event structure, FPGA programming highlights, data accumulation specifications, and general module specifications and performance benchmarks