= 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||<:-4>TDC ID||<:-12>event number||<:-12>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||<:-4>TDC ID||<:-12>event number||<:-12>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||<:-4>TDC ID||<:-5>channel||<:-19>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||<:-4>TDC ID||<:-5>channel||<:-7>width||<:-12>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||<:-2>0||<:-2>device||<:-9>reserved||<:-15>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 [[http://tdc.web.cern.ch/tdc/hptdc/docs/hptdc_manual_ver2.2.pdf|HPTDC manual]].