# Prevent ISE from bitswapping the configuration file

For some reason unknown to me, ISE provides a bitswapped configuration image: each byte has its bits swapped.

Is there a way to disable this bitswapping? (Having to do it again in C code slows down the image loading.) I've had a look at the Bitgen options and was surprised to not see what I wanted there.

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You mentioned selectmap in the tags. Is that how you are loading the bit file? –  Brian Carlton Jul 30 '12 at 16:39
@BrianCarlton: Yes. It's more convenient in my case (given the hardware configuration) for the bits to be in the reverse direction –  Randomblue Jul 30 '12 at 16:57

You need to feed PROMGen the -b option to disable bit swapping. This is described in the Command Line Tools User Guide in Chapter 17, page 255. But it also describes how to access PROMGen in the Project Navigator (ISE) GUI.

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Thanks, but it seems that the option is not a compilation option for ISE, but rather for iMPACT after compilation, as an extra step. I just want my .bin files without bit-swapping produced during compilation. –  Randomblue Jul 31 '12 at 9:10
I got confused by the statement, "There is also an interactive version, called the PROM formatting wizard that you can access from inside Project Navigator (see the iMPACT Help)." Since it mentioned Project Navigator, I assumed there was a setting in ISE. But you're right, it's in iMPACT. Or via command line –  embedded.kyle Jul 31 '12 at 13:01