GPIO endianness on MPC8349

Kumar Gala galak at
Tue Apr 11 06:06:33 EST 2006

On Apr 10, 2006, at 2:48 PM, Ben Warren wrote:

> Hello,
> I'm a noobie to this CPU, and am utterly confused with how the bits  
> are
> ordered on the GPIO ports.  I imagine it's the same as all Freescale
> PPCs, but who knows.  Anyway...
> Using an MPC8349MDS eval board, I have one LED to play with.  From the
> schematic, it's connected to GPIO1[1].  From other processors that  
> I've
> worked with, I would have expected to toggle it with either 0x40000000
> (IBM 405) or 0x00000002 (68360).  Nope.  To make this bit move, I mess
> with bit 0x00000040 in the appropriate DAT register.  This leads me to
> believe that either the bit ordering is something
> like ...89abcdef01234567 (sorry for the confusing notation, but
> hopefully it makes sense) or the schematic has a typo.  Since I'm  
> trying
> to write a generic GPIO handler, I'd like to have a little  
> confidence in
> my extrapolation from a single point.
> Can anybody shed some light on this?

This is because the Freescale docs are misleading.  If you look at  
the schematic you will see the LED is wired to GPIO1[5] which makes  
sense for the 0x40 value you have to use.

- kumar

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