TPC data formats

The data from the BRAHMS TPC will be read by the STAR readout board and transmitted to the BRAHMS receiver board which will performe pedestal suppresion and data compaction.More details on this is given in Karim Ashktorabs preliminary description of the receiver board.

Some of the basic features are

• Raw uncompressed data. These will contain for each pad and time samples (ADC values) as 10 bit data stored in 16 bit words. These will be quite large e.g. 1152 pad * 128 or 256 time sample. They will mainly be used to chekc detector performance, and create pedestal values.
• Pedestal subtracted data It is envisioned that these might appear either as 10bit or 8 bit data. The 8 bit data can be expected if a non-linear transformation for 10bit to 8 bit is performed in the VME processors before the events are build and send to the data store.

The data should probably be arranged with the following information

The data will come from 4 TPCs. The two TPCs in the MRS will have 1152 pads in 12 and 6-7 rows respectively. The FS TPC will each have about 768 pads arrenged in 12 and 6 rows respectively. To get more information on the expected pad layout see the documenton the TPC design.

One way of arranging this would be in the following format:

	short pad#	Padnumber (0-1151) 
	short timeslice start (0-511)
	short number of samples (0-511)
      Short sample 1
	short sample 2
    ....

Since the BRAHMS TPC and the STAR TPC share the same readout system there is obvious a potential large overlap between the formats that we and STAR use. Some information on the STAR formats and the different data which can be expected from the readout boards are given in STAR note 282.