I just discovered a small error in the domino brochure. The Domino Pins Features table shows Di10 as an interrupt capable pin. When Intellsense did not show it as such in FEZ_Pin.Interrupt I peeked at the Domino schematic and saw it was indeed not an interrupt capable pin.
Anyhow not a big deal for my purposes, I can use An3. I’m making a simple cable tester and need to be able to use as many tristate pins as possible. In the future I’m going to use some SPI controlled analog switches like the ADG725/ADG731 to increase the number of test points.