the above mentioned signal screening is implemented by the wfsc as it is explained below the mask detection arithmometrs 11 mda and 12 mda for the wfsc are positioned similarly as the dfas of the nfed the second stage uses the mask detection arithmometers 11 mda 12 mda for identifying wave forms which are beyond usually acceptable range defined by the pcu the programmable control unit pcu determines logical and or arithmetical processing which the 11 mda 12 mda shall perform by pre loading the detection control register dcr with a control code applied as the dcr p 0 to the 11 mda 12 mda additionally the pcu determines the mask dmr r 0 which the captured data 11 wb r 0 12 wb r 0 shall be processed against by pre loading the detection mask register dmr the 11 sel signal equal to 1 0 selects the 11 wb r 0 12 wb r 0 to be downloaded to the phase one detected data buffer 1 ddb by the clock 1 clk 2 see fig1 and fig1 if the 11 det 12 det indicate detection of a pre selected mask by the mask detection arithmometer 11 dma 12 dma at the beginning of the next time frame which has 128 phase 1 cycles the last captured 1 ddb content is further downloaded to the phase 1 data register 1 ddr by the clock signal 1 clk 3 128 number of said mask detections is counted in the mask counter buffer 1 mcb as it is explained below at the beginning of every time.