TDC Raw Data Format

Data read out of the TDC is contained in 32 bit data packets. The first four bits of a packet are used to define the type of data packet. The following 4 bits are used to identify the ID of the TDC chip (programmable) generating the data. Only 8 out of the possible 16 packet types are defined for TDC data (bit 31 always set to zero by TDC). The remaining 8 packet types are available for data packets added by higher levels of the DAQ system.

Data types:

0010 - TDC header
0011 - TDC trailer
0101 - TDC leading edge time measurement
0110 - TDC trailing edge time measurement
0110 - TDC error

0010 - TDC event header

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	1	0	TDC ID				event number												TDC timestamp

TDC ID is the programmed ID of TDC

TDC timestamp in number of 25 ns time intervals since global trigger timestamp found in event header.

0011 - TDC event trailer

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	1	1	TDC ID				event number												TDC word count

0101 - TDC leading measurement

0110 - TDC trailing measurement

Time measurement data format depends on resolution set.

Single edge measurements:

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	1	0	1	TDC ID				channel					time measurement

channel - TDC channel number, 0 to 31
time measurement - leading or trailing edge measurement in programmed time resolution

Combined leading and trailing measurement, pairing mode

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	1	0	1	TDC ID				channel					width							leading time

width - pulse width in programmed time resolution
leading time - leading edge measurement in programmed time resolution

0110 - TDC error

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	1	0	0		device		reserved									TDC error flags

TDC error flags bits:

[0] Hit lost in group 0 from read-out fifo overflow
[1] Hit lost in group 0 from L1 buffer overflow
[2] Hit error have been detected in group 0
[3] Hit lost in group 1 from read-out fifo overflow
[4] Hit lost in group 1 from L1 buffer overflow
[5] Hit error have been detected in group 1
[6] Hit lost in group 2 from read-out fifo overflow
[7] Hit lost in group 2 from L1 buffer overflow
[8] Hit error have been detected in group 2
[9] Hit lost in group 3 from read-out fifo overflow
[10] Hit lost in group 3 from L1 buffer overflow
[11] Hit error have been detected in group 3
[12] Hits rejected because of programmed event size limit
[13] Event lost (trigger FIFO ovefrlow)
[14] Internal fatal chip error has been detected

Most important error bits are 12 and 13. Error bit 14 should be ignored.

For detailed description of TDC please refer to HPTDC manual.