RAMPS uses pin headers, which are not polarised and have a habit of falling off. Duet uses Molex KK series connectors, which are polarised to stop you connecting them the wrong way round (very important when building a kit using ore-made cables) and locking to stop them falling off.
That said, it is possible to plug the cables from a RAMPS setup into the Duet, because the pin spacing and size are the same. The motor connectors can be plugged in directly. However, the endstop connections are different. For 2-wire microswitch endstops, the Duet uses the two outer pins of the 3-pin connector, instead of the middle pin and one outer pin as RAMPS does. This avoids the problem you get with RAMPS whereby if you plug the connector in the wrong way round, you short out the 5V rail.
Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod
Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
