2.1.6 Power distributionThere are two ways in which the board can get its main powersupply (3.3V) when it is plugged into the VME crate:Directly from the VME backplane.Getting 5V from the VME back plane and converting thisvoltage into 3.3V with a DC/DC converter (PT5801).Furthermore, an ADP3330-2.5 DC/DC voltage converter is used toget the 2.5V voltage needed for the VME-FPGA from the +5V backplanesupply.In addition, the ±12V and ±5V lines in the VME backplane areused by the trigger/busy logic.Finally there are two +5V and GND connectors to be used withan external power supply for debugging tasks. It is possible to select thepower supply mode by placing a fuse in one of two fuse holders (labeledas VME FUSE and CONVERTER FUSE). It is very important not toplace the two fuses simultaneously. VME FUSE must be placed to getpower from the VME bus (board plugged in the crate) whereasCONVERTER FUSE must be placed to get power from the externalsupply.2.1.7 Data distributionThere are two different functioning modes in the OMB: CRCprocessing mode and data injection mode. Figure 3 shows the datadistribution in the CRC mode. Two connectors receive the data and6
route them to the CRC-FPGA. Then, the CRC is checked and thedecision is taken on which data is send to the ROD. Every time a CRCerror is detected it is communicated to the VME-FPGA and the errorcounter is incremented. The values of these error counters can be readout in real time through the VME bus.Figure 3:Data distribution in CRC mode.Figure 4 shows the data distribution in the data injection mode inwhich the optical receivers are not used. There are two differentinjection modes:Counter mode: The events have all words with the same valueand this value is incremented with each event sent.Memory injection mode: The events sent are previously storedin the internal memory.In both cases the events are sent every time a trigger is receivedin the CRC_FPGA either by the external LEMO connector in the frontpanel or by VME. We will describe these data injection modes in moredetail in section 3.1.1. 7
Figure 4:Data distribution in Injector mode.2.1.8 Trigger and busy handlingThe trigger signals used to select the injection rate can begenerated either from an external source or they be generatedinternally in the VME FPGA. If the external mode is selected the triggeris received by the OMB through a lemo connector placed in the frontpanel which is connected directly to each CRC-FPGA. Both triggermodes and other specifications about trigger operation modes will becompletely described in section 3.1.2. The busy lemo connector can receive an input signal that can beused to receive a busy signal from the Trigger and Busy Module (TBM)to stop the data injection if at least one ROD is in busy state . Thebusy lemo connector is directly connected to each CRC-FPGA and to theVME-FPGA.
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Cyclic redundancy check, Data acquisition, OMB, VMEbus