When I initialize the JTAG chain targeting the Virtex-4 FF668 AFX board, the XCF32P PROM is not seen in the chain. The JTAG chain jumper is set to include both PROM and FPGA, so why does the PROM not show up? Additionally, when I attempt to program or do any JTAG operations, such as IDcode check, they fail. Why?
The initial production run of the FF668 AFX boards was assembled with the STMicro ES high-density PROMs. Because of the errata associated with the ramp rate, most power sources for the board failed to meet this specification. This can be easily resolved by removing the PROM Power VCCINT jumper and replacing it. Because voltage is already being applied to the board, the ramp rate requirement is satisfied. Launch iMPACT and initialize the chain. At this point, both PROM and FPGA should be seen and all JTAG functionality should be correct. Later production runs of these boards will include ESB or production Platform Flash PROMs in which the errata is not applicable.