hi, I have a custom designed board with spartan 2 (XC2S150) with some input data and clk line connected to a peripheral device, the clk level is 3.3V and FPGA IO standard(not defined in .ucf file so is the default) is LVTTL and VCCIO is 3.3 and VREF of FPGA is not connected to any voltage.
my problem is, sometimes reading data from peripheral is erroneous and after some test I'm sure that the GND level of peripheral and FPGA is changing so that some clk edges are missed in FPGA which result in the data corruption. inorder to resolve this problem, I connected the two board with a good ground wire and after that there was fewer data loss but not 100% correct. another thing that I wanted to do is changing input IO Level from LVTTL to LVCMOS2.5, but I'm not sure if it is possible regarding that the VCCIO is connected to 3.3V? how should I know that the level of FPGA is working at LVCMOS2.5?
is this presumtion going to fix my problem? tnx in advance for any helpful comment, Neda Baheri
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