09-24-2009 03:14 AM
I have a SPARTAN3 XC3S5000 and I have some banks with IOSTANDARD = LVDCI_33 constraint.
How mach current does the FPGA supply with this type of IOSTANDARD = LVDCI_33?
Can't I set the current that the pins with IOSTANDARD = LVDCI_33 constraint supply by option "| drive = 16 or others values?
The Map report doesn't consider the constraint " drive = 16" or others value when I use the IOSTANDARD = LVDCI_33 constraint. Why?
09-24-2009 03:46 AM
I suppose that Xilinx decided to implement full drive strength when using DCI.
Drive strength can be used to improve signal integrity when no internal nor external termination is used. When termination is used drive strength isn’t of concern because serial termination resistor is the one that limit the “actual” strength and of course the one that matches the output impedance with transmission line characteristic impedance.
09-24-2009 01:23 PM
Another way to look at this is that the drive strength in DCI mode is set by the external resistors,
so you don't need to select it using constraints.