# Interferences of Electromagnetic Pulses on Microcontroller Units
## 3 Experimental Protocol  
The integrated circuit (IC) chip was placed in the center of the test plate (Figure 1) and transferred to the workspace of the TEM cell during the test (Figure 6). Solder was applied between the test plate and the TEM test window to ensure good initial contact. The remaining components were placed on the back of the test plate and came in surface mount packages.  
1. An oscilloscope was used to monitor pins 34 and 44 of the MCU. When the MCU was working normally, pin 44 output a PWM pulse, and pin 34 produced a communication signal level at a regular time interval. The reason for choosing these two pins is because the system clock is used to coordinate and control various inputs and outputs of the system, and generally uses rising edge triggering, making it very sensitive to instantaneous electromagnetic interference. Pin 44 can serve as an output observation window. In addition, another port of the oscilloscope was used to monitor the output waveform of the EMP simulator.
2. The MCU was placed in the TEM cell while in working condition. Each time a set of data was measured, the plate was rotated 90\({}^{\circ}\) counterclockwise, and the measurement was repeated under the same conditions. Hence, measurements were collected at a total of four positions. Please note that when pins 1-11 were parallel with the \(x\)-axis of the TEM cell, the angle was defined as 0\({}^{\circ}\).
3. During the test, different storage capacitors were used to change the FWHM of the pulse, and the breakdown voltage was adjusted by changing the pressure of the air gap switch at the power source (i.e., the amplitude of the voltage).
4. Starting from the smallest storage capacitance, the initial air pressure was 1 atm, and the electrode distance was 2 mm, which remained constant. Each group of tests was repeated three times, and then the air pressure was increased by 1 atm until the pressure reached 4 atm. Then, the test plate was rotated, and the above tests were repeated. After all tests at four positions were completed, the storage capacitor was replaced. A total of three storage capacitors were used in this study.  
The oscilloscope had a bandwidth of 500 MHz, and Figure 6 shows the test setup. The connection method of the test piece is shown in the upper-right corner of the figure. In the experiment, it is obvious that the EMC and oscilloscope cable also have a coupling effect. However, this coupling effect can be ignored relative to the MCU, mainly because the shielding structure design of the oscilloscope cable (including input impedance matching and coaxial structure) can effectively eliminate this coupling. In addition, the non-negligible length of cable can effectively attenuate the electromagnetic pulse conducted by coupling.  
Figure 6: Test setup.  
2. Output waveform Figures 7 and 8 show the output pulses of pins 34 and 44 with and without interference. It can be seen from Figure 7 that when the EMP simulator was not working, the outputs of pins 34 and 44 were normal. When the EMP simulator output EMPs, as shown in Figure 8, there was a strong interference signal (red and blue pulses). Specifically, pin 34 had a decaying oscillation waveform, whereas pin 44 had a spike similar to the electric waveform. It is worth noting that at this time, pin 34 was outputting a 0-level communication clock signal, but the interference signal may affect the communication clock of the MCU. The amplitude