This may be an odd question but here goes...
I would like to use the JTAG chain to program Xilinx's Virtex-II fpga and the Platform Flash ISP Configuration PROM. OK, that's not a problem as it's detailed in document DS123 (v2.2). However, I would like to add a second Platform Flash PROM in the same chain as the Virtex-II and it's config PROM. This second PROM would be used to hold general purpose data (ie. not FPGA config data). I would like to connect this PROM to unused I/O of the FPGA which would then reset the PROM and pull data out of it serially to be used in other parts of the product we're developing.
Each "box" we're designing will have analog control bits that need to be tweaked when the unit is sealed up. The only access I have to the PROM is through the JTAG interface. I was wondering if anyone has seen any app notes detailing this sort of interface/design.