Abstract
Since the launch of the SWIFT, Gamma-Ray Bursts (GRBs) science has been much progressed. Especially supporting
many measurements of GRB events and sharing them with other telescopes by the Gamma-ray Coordinate Network
(GCN) have resulted the richness of GRB events, however, only a few of GRB events have been measured within a
minute after the gamma ray signal. This lack of sub-minute data limits the study for the characteristics of the UV-optical
light curve of the short-hard type GRB and the fast-rising GRB. Therefore, we have developed the telescope named the
Ultra-Fast Flash Observatory (UFFO) Pathfinder, to take the sub-minute data for the early photons from GRB. The
UFFO Pathfinder has a coded-mask X-ray camera to search the GRB location by the UBAT trigger algorithm. To
determine the direction of GRB as soon as possible it requires the fast processing. We have ultimately implemented all
algorithms in field programmable gate arrays (FPGA) without microprocessor. Although FPGA, when compared with
microprocessor, is generally estimated to support the fast processing rather than the complex processing, we have
developed the implementation to overcome the disadvantage and to maximize the advantage. That is to measure the
location as accurate as possible and to determine the location within the sub-second timescale. In the particular case for a
accuracy of the X-ray trigger, it requires special information from the satellite based on the UFFO central control system.
We present the implementation of the UBAT trigger algorithm as well as the readout system of the UFFO Pathfinder.
