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The XL1 card takes standard VME A<31..1
address lines along with
the six address modifier (AM<5..0) lines, the Longword, DS0, DS1,
and the AS control lines and decodes acceptable register and
memory addresses for the SNObus crate(s) attached to the particular
XL1 card in question. Each XL1 card can deal with one to four SNObus
crates through an XL2 card in each SNObus crate. Thus a maximally
dense system would require only five XL1 cards to deal with 20 SNObus crates.
The address translation is such that a single VME167 SBC should be able
to address any of 10,000 electronics channels through a single VME
backplane. In actual practice the XL1 cards are likely to master for
only one or two crates and there are likely to be two to four
DAQ VME bus crates with XL1 and VME167 cards at the first DAQ layer.
The XL1 card recognizes only two AM combinations - one for Register
Space and one for Memory Space. While the AM decode logic is embedded
in a Xilinx reprogrammable FPGA and could be changed to some other
pattern, the present design is for:
