I am using the C5510 and want to use the GPIO pins in an open
collector mode.  I know that in general, it is possible to set the
output data register to a 0 and toggle the output enable (direction)
bit to allow the output to drive a 0 or to tristate and let a pullup
put a 1 on the signal.  But the info in the C5510 data book is not
clear if you can do this without driving a 1 momentarily.  It
indicates that you can only write to the data register when in output
mode.  So if the data register is a 1, the output will be driving a 1
momentarily until you can write a 0 to the data register.  

I asked my local FAE about this and he contacted the "factory".  Three
opinions said I could not use the port the way I want.  I still don't
belive them, but I don't have a DSK yet to test this on.  Anyone know
for sure if the GPIO port on the C5510 will work this way, allowing me
to write a 0 to the output data register while the direction register
is still in input mode?