Hi i am designing a board that will connect to a pci-x single board computer directly (without backplanes) via PICMG 1.0 edge connector in the sbc, problem is that IDSEL is not direcly available on the Card Edge Pins, the PICMG 1.0 Specification tells that IDSEL1's must be routed with AD31 for backplane slot 1, IDSEL2 with AD30 etc. right? and btw, what does 2U in PCI-X Backplanes means?
Thanks.
No idea about PCI-X, but 2U is a height measurement of about 3.5 inches.
2U means 2 units of 19" rack equipment height. 3.5 inches.
Graham
Normally during a command cycle all of the targets look at AD0..31 (or up to 63 for 64 bit) to decide if the address falls within their mapped space(s). However, if the command is config read or config write, then it looks exclusively at IDSEL and AD0..1 to decide if it's selected. Then, within the config space, only the lower address bits are used because the config space is small. For that reason, many bridge chipsets use AD16..31 as IDSEL lines, connecting them to the individual slots. That's not required by the spec, it's just a common feature of PCI bridge chipsets.
-- Ben Jackson AD7GD http://www.ben.com/
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