R2E 1st Combined Workshop & School Days, 2-3 June 2009 "SEU Tolerance in the ELMB", H.Boterenbrood Summary -------- The Embedded Local Monitor Board (ELMB) is a programmable plug-on microcontroller module designed as a general-purpose building block for monitoring and control tasks in the ATLAS experiment. The ELMB has found a number of applications in and around the other LHC experiments as well. The ELMB is composed of standard COTS components, no special rad-tolerant or rad-hard components were used. The ELMB comes installed with ready-to-use firmware for control of digital I/O and analog inputs. It communicates via a CAN bus utilizing the CANopen protocol. Users can develop their own custom application software, supported by low-cost tools and the existing source code as example. As the ELMB is meant also for use inside the experimental cavern -in ATLAS not closer to the interaction point than the region outside the calorimeters- qualification for the expected radiation levels is required. A series of radiation tests have been done with the ELMB, focusing on each one of the radiation effects of TID, NIEL and Single Event Effects (SEE). Single Event Upsets (SEUs) in the ELMB have been studied in a working ELMB, both systematically, by scanning for changes in preset bit patterns in its memories and registers, as well as functionally, by looking for anomalous behaviour and deciding on the action to recover from it, if necessary. In the SEU tests of the ELMB we found that SEUs occur in SRAM and device registers. The software for the ELMB has been written with a number of adaptations to take this into account, such as majority voting, register refresh, and others. In the SEU tests of the ELMB we did not find any SEUs in EEPROM or FLASH memory. The software has been adapted to take advantage of this fact by using the EEPROM as a kind of rad-tolerant extension to the SRAM for storing long-lived variables. The extra precautions taken in writing the ELMB software contribute to mitigate the effects of SEUs in the module and increase the overall tolerance of the ELMB to SEUs.