FAST VERTEX DATA FROM THE LEVEL ZERO TRIGGER ----------------------------------------------- Daniel Edmunds Revised 7-FEB-1990 This note is the final specification of the Fast Vertex Data that will come from the Level 0 Trigger and go to the Level 1 Trigger. The Level 0 system will provide a 5 bit two's complement fast vertex Z position to the L1 Trigger. The sign of this two's complement number will indicate the direction of the vertex from Z = 0 in the standard D0 coordinate system (i.e. positive Z is in the direction that the protons travel or South at D0). The least significant bit of this 5 bit number represents 6.25 cm along the Z axis. When this 5 bit number is zero it will indicate that the vertex was within a 6.25 cm wide bin that is centered at Z = 0 of the standard D0 coordinate system. There are 15 bins in the positive Z direction centered at locations 6.25 cm, 12.5 cm, ... , 87.5 cm, 93.75 cm. Each bin is 6.25 cm wide. There are also 15 bins in the negative Z direction. The negative bins are centered at the same absolute displacements from Z = 0 as are the positive bins. The "extra" negative bin, due to two's complement numbering, is not used. Besides the 5 bit number there are 2 additional signals that flow from the Level 0 Trigger to the Level 1 Trigger. The first of these control signals, called the Good Signal, is used to indicate that the Level 0 system was successful in calculating a Fast Vertex Position for the current beam crossing. If the Level 0 system is not successful in calculating a Fast Vertex Position (e.g. because there was no interaction during the current beam crossing or because the interaction vertex was outside of the defined bins coverage) then this control signal will not be asserted and the 5 bit two's complement vertex position number will be set to zero. The second of the control signals is a strobe signal that indicated that there is stable new data on the other 6 lines. The Level 1 Trigger may use the positive edge of this strobe signal to clock a latch that holds the other 6 signals. The following table describes the cable pinout that carries all of the signals described above. All signals are differential ECL levels. The pull down current sources are provided at the driving end and the lines must be terminated with a 110 ohm resistor at the receiving end. LEVEL 0 TRIGGER FAST VERTEX DATA TO THE LEVEL 1 TRIGGER --------------------------------------------------------- PIN # CABLE COLOR SIGNAL MNEMONIC ------- ------------- -------- ---------- 1 BROWN Z DATA 0 NON-INVERTED LSB NZ0 2 TAN Z DATA 0 INVERTED LSB IZ0 3 RED Z DATA 1 NON-INVERTED NZ1 4 TAN Z DATA 1 INVERTED IZ1 5 ORANGE Z DATA 2 NON-INVERTED NZ2 6 TAN Z DATA 2 INVERTED IZ2 7 YELLOW Z DATA 3 NON-INVERTED NZ3 8 TAN Z DATA 3 INVERTED IZ3 9 GREEN Z DATA 4 NON-INVERTED NZ4 10 TAN Z DATA 4 INVERTED IZ4 11 BLUE GOOD NON-INVERTED NGOOD 12 TAN GOOD INVERTED IGOOD 13 VIOLET STROBE NON-INVERTED NSTRB 14 TAN STROBE INVERTED ISTRB 15 GREY no connection 16 TAN no connection 17 WHITE no connection 18 TAN no connection 19 BLACK GROUND AT SENDING END OPEN AT RECEIVING END 20 TAN GROUND AT SENDING END OPEN AT RECEIVING END