HFB: A Fast Bus Multi Event Double Port Buffer Memory

We describe here the FB [ 1 ] double port buffer memory developped 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 developped by G. Fremont [ 2 ] 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 DATASpace on the port "A", and a flag to choose between them, to allow for a FB spying of Data during the DAS dead time.