issue on on using Xilinx PROMS in conjugation with System ACE;

Hello,

I am currently working on a board design based on Virtex-4 FPGAs. For configuration I am planning to use 4 XCF32P(parallel platform flash) and a system ACE chip so that I can have two options to program.

I have 2 virtex-4 fpga's (LX200), 4 platform flash and system ace controller in jtag chain.

The JTAG chain is as follows: PC4 CONN -> System ACE -> PROM3 -> PROM2 -> PROM1 -> PROM0 -> FPGA1 ->

FPGA2 -> PC4 CONN(back)

I am planning to use either jtag, master serial(proms) or system ace modes of configuration.

The fpga Mode setting bits for configuration: M2 M1 M0

1 0 1 - Jtag 0 0 0 - Master serial 1 1 1 - System ACE ?

In addition to this settings I need a extra switch to select between platform proms and system ACE (as described in ML401 Board documentation and schematic) configuration modes.

This switch is two way in sense that it disables system ace and enables platform proms and in other action disables platform proms and enables system ace.

--- use system ace and disable proms --- Normally for cascade configuration of PROMS, the fpga_done pin from fpga goes to 1st prom0 ce_bar, the ceo of prom0 goes to ce_bar of prom1, the ceo of prom1 goes to ce_bar of prom2, the ceo of prom2 goes to ce_bar of prom3 and the ceo of prom3 is left unconnected.

So if I want to disable these prom chain(when using system ace), then I need to disconnect fpga_done from ce_bar of prom0 and connect to VCC ?

Do I need to connect all ce_bar (PROM0, PROM1, PROM2, PROM3) to VCC or for PROM0 will do ?

--- use proms and disable system ace --- connect CFGMODEPIN of system ACE to gnd ?

I appreciate if any one can respond.

Regards Nannapaneni

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