HFB : A FASTBUS multi event double port buffer memory

The authors describe here the FB double port buffer memory developed at the LPNHE of the University Paris VI. Its purposes are to make available same features useful in the High Energy environment, to reduce, for a given amount of memory, the dead time data collection in a large size (in term of read-out channels) High Energy experiment and to get a buffer of memory as cheap and reliable as possible. The FB protocol, on the crate and cable side, is exploited using the coupler on 4 PAL's developed by G.Fremont and E.Sanchis. The DATA-Space is divided in 4 independent smaller blocks in a way such that a block can be accessed from a port while a different block is accessed from the other port. The two ports are: A, the FB crate port and B, the FB cable port. The buffer works as a rotary FIFO, looping over the 4 blocks of memory, but allowing for any random access. A mechanism is implemented on the board in order to be able to link different modules placed everywhere. If there are m modules, the looping will be around m 4 memory blocks. A multi event function is implemented on the board. HFB is quiped of two NTA for the DATA-Space on the port ''A'', and a flag to choose between them, to allow for a FB spying of DATA during the DAS dead time. HFB is a buffer of memory which can be used at each stage of a DAS: Frontend, Intermediate (MEB) or final, being completely FB standard. The HFB was designed for the LEP data acquisition system