Folks, due to the use of channel multiplexors on T4 and T5, and the funny wiring scheme from chambers to TDCs, we need to modify the currently standing "one record per plane" scheme. The multiplexors join the signals from two wires into one TDC channel: one wire is delayed, the other is "prompt". The main problem is that in all planes some wires are "prompt" and some are "delayed", and the demultiplexing cannot be trivially handled by the unpacking in the event builder. It will have to be handled by code in BRAT. To tell the BRAT code which wires are prompt and which are delayed, I propose to change the encoding of wire numbers: prompt wires 1 through 99 are defined as channel numbers 1 through 99 (same as T3). delayed wires 1 through 99 are defined as channel numbers 101 through 199. Example: in a T4 plane record, channel number "5" means "wire 5, prompt", channel number "122" means "wire 22, delayed". This scheme works because TDC records have 8 bits for channel numbers (0..255) and none of the T4,T5 planes have more than 99 wires. The current unpacking software in BRAT will need to be modified to take wire numbers modulus 100, and to account for the shifted timing for the delayed wires. Baring better suggestions, I will implement the final T4 and T5 mapping according to this scheme. -- Konstantin Olchanski Physics Department, Brookhaven National Laboratory, Long Island, New York olchansk@bnl.gov
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