Tuesday, November 17, 2009

FCS Bin Size - Board #2

New FCS hardware and firmware now provide the FCS application-level software the option of choosing one or two data channels. Lisa measured and verified the actual time bin sizes generated from the new board.

The bin sizes for one-channel mode are 0.4801 μs, 1.0002 μs, 2.0003 μs and 5.0007 μs. For two-channel mode, the values are 0.8201 μs, 1.0002 μs, 2.0003 μs and 5.0007 μs.

Tuesday, November 3, 2009

FCS Bin Size - Board #1

The FCS software provides four different user-selectable bin sizes. Nominally, the available bin sizes are 0.8 μs, 1 μs, 2 μs, and 5 μs. The actual bin sizes will be slightly different because of how they are calculated in the firmware. (I will go into more detail on this below.) In reality, the bin sizes used by the software are 0.818 μs, 0.998 μs, 1.995 μs, and 5.009 μs.

The FCS hardware is controlled with an SX48 microprocessor, and the different bin sizes are generated by adding or removing instruction cycles to the SX code. The SX uses a 50MHz crystal, so each instruction cycle is 20 ns. These actual bin sizes are the closest we could get to the ideal values given the 20 ns resolution. The code for the 0.818 μs bin size has no delay cycles added, so this is the smallest possible bin size.