iMX31 ARM Processor

I am working on a project with the iMX31 processor. I have seen some posts in this group about people using this processor so I hope someone can help out. I need to tri-state a GPIO pin in this processor. I have looked in the Reference Manual and it doesn't mention any option to set it in tri-state. Essentially this is for a case where an external line is connected to the same pin as the iMX and only one of them can be driving the line. In case the iMX processor isn't driving the line it must be tristated. I hope someone who has used this processor before can help me out on this. Thanks.