The trigger primitive signals go from the FECs to the Trigger Card via four busses and four sets of point to point lines. The four busses are the top and bottom (of the FEC and backplane) high and low gain energy sums - the bus acts as part of a crate-wide current summing node. The NHit signals are carried as point to point lines in order to preserve maximal timing information and to maintain a reasonably high quality transmission line environment. The NHit100 and NHit20, top and bottom signals are brought together into final NHit100 and NHit20 sums on the Trigger Card after being properly terminated at the card.
The trigger primitives are summed on the Trigger card and then sent to the Masteror Central Trigger crate which produces Global Trigger, SynchClr, SynchClr24, and Test Time signals. These four timing signals are then sent out to each of the Trigger cards (via differential ECL) and then rebroadcast across the SNObus by the Trigger card, again, in differential ECL form.