Undergraduate Research at Jefferson Lab

Improving FADC-250 Test Code with the Implementation of a Fan Out Board

Student: Rachel Malonson

School: Christopher Newport University

Mentored By: Hai Dong

Flash analog to digital converters (FADC's) are used to convert analog signals to digital signals which can be interpreted and stored by a computer. At Jefferson Lab, FADCs clocked at 250 Mega Hertz (FADC-250) are used to collect and process data in all of the experimental halls. Because these converters are so important in collecting information about experiments, it is essential that they are tested thoroughly before being put into the field. To test the converters, they are placed into a Virtual Machine Environment (VME) bus-switched serial standard, or VXS, crate and connected to a XILINX cord, which is connected to a computer. The XILINX cord is used to communicate between the FADC-250 and the C++ code written to test the converter. The purpose of this project was to modify the test stand to simplify the testing process and reduce the time to debug the FADC-250 boards. The first step in improving the testing of these boards was to program a fan out board to send the same analog signals to all sixteen converter inputs. This was accomplished by writing to a memory with 32 locations that holds 32 'points' that would create a waveform. Buttons to make each test run continuously were then added by implementing a new timer and Boolean variables for each test to determine whether the test should be run. The modified test code now allows the user to test all sixteen analog to digital converters (ADCs) with the click of one button and continuously run each ADC test and other tests for debugging purposes. If any test fails, it also displays to the user information about why the board failed, such as what the expected result was and what the actual result was. The addition of the fan out board and button to run all of the ADC tests at once will allow for much faster testing. The user will be able to run all of the ADC tests at once using the fan out board. Finding the exact problems with each board will be easier because the user will be able to run each test continuously while probing the board and the results from each failed test will be displayed. The improved testing of the FADC-250 boards will allow for quicker fixing of problematic boards and increase the amount of boards readily available for use in the field.