onnel using a keyboard and monitor extension, but all high speed test equipment and control equipment had to be placed in the target room. Whenever test equipment must be located near the target it is a good, if not necessary, precaution to be aware of the possibility of scattered protons and neutrons reaching the equipment and place more sensitive units where the exposures will be minimized. IV-25 The previous example described the evaluation of a commercially available device that was being considered for flight. Often, the interest is in the proton SEE characteristics of a technology, and test circuits may be used resulting in simplification of DUT interfaces. Examples are described in [Mars-95 and Reed-96] along with data showing the importance of going to the trouble of the high speed test approach. Figure 11a illustrates that significant differences in proton upset sensitivity for static versus dynamic testing can result as the data rates enter the hundreds of Mbps regime. The explanation is based on an enhanced sensitivity as data transitions near clock edges, and this is carefully mapped out in [Reed-96]. In general, it is important to test a device with as much fidelity as possible to the intended application, and this is especially important with regard to clock speed where high data rates are required. Design of test hardware and DUT fixtures for high data rates is challenging in itself, and misleading results can follow from bandwidth-limited test configurations [Reed-96]. For this reason, broadband test sets with excess bandwidth are highly recommended. Proton Cross-section Speed Dependence SCFL Static SEU Test SCFL 400 Mbps 10-10 10-11 Proton Energy (MeV) Figure 11a. Bit error rate testing of GaAs HIGFET shift registers showed that static upset measurements would underpredict the upset rates by large factors if the intended application involves fast clock speeds [Mars-95]. These factors increase as the data rates increase and can approach 100. 4.1.2 Small Probability Events: A recent Short Course [P