Cornelius DPC 230 Especificaciones descargar pdf (Pagina 62)

56 SPCM Software

loss of photons or any loss in photon information. Pre-processed data are identified by

‘RAW = 0’. The description given below relates to pre-processed data.

Time per bin

TPB[23:0] defines the time unit in which all subsequent photon data are expressed. TPB is

given in femtoseonds. All times are expressed in multiples of TPB.

Records of Photons

The records following the descriptor are photon data. All detection events are recorded with

their channel number and a 54 bit integer time stamp. The time stamp reflects the absolute

time from the start of the measurement. The time unit is the TPB entry in the descriptor, see

Table 2.

To save disk space an event is normally stored with its detector channel number and the lower

24 bit of the time tag only. Only if the time in these 24 bits overflows the complete time is

written. The bits 30 and 31 are used to identify whether the record is a photon with a 24 bit

time or a record containing the higher bytes of the time of the previous photon. The meaning

of bit 30 and bit 31 are shown in Table 3.

Bit 31 Bit 30 Type Description

0 0 Event Low Part of Time [TPB] incl. channel number

0 1 TIME[53:24] Set Time to TIME[53:24]

1 0 Reserved Reserved

1 1 Special Descriptor, at start of file

Table 3: Bits identifying whether a record contains a 24 bit time or the higher bits for the complete 54 bit time

Event Record

The format of a photon record with 24-bit time is shown in Table 4.

Bit 31 Bit 30 Bit 29 Bit 28 Bit 27 Bit 26 Bit 25 Bit 24

0 0 GAP Ch[4] CH[3] CH[2] CH[1] CH[0]

Bit 23 Bit 22 Bit 21 Bit 20 Bit 19 Bit 18 Bit 17 Bit 16

TIME[23] TIME[22] TIME[21] TIME[20] TIME[19] TIME[18] TIME[17] TIME[16]

Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8

TIME[15] TIME[14] TIME[13] TIME[12] TIME[11] TIME[10] TIME[9] TIME[8]

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

TIME[7] TIME[6] TIME[5] TIME[4] TIME[3] TIME[2] TIME[1] TIME[0]

Table 4: Photon record (24 bit time)

CH[4:0] Channel number of the DPC in which the photon was recorded. The LVTTL

have channel number from 1 to 16, the CFD channels have the channel numbers

1 and 2 for TDC 1 and 11 and 12 for TDC 2, see Fig. 77, page 47.

TIME[23:0] Event Time [TPB], low part. Only if bit 30 and bit 31 are 0, i.e. the higher part of

the time has not changed.

GAP The FIFO has overflown. Data of a number of photons were lost before this en-

try.

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Cornelius DPC 230 Especificaciones Pagina 62