Hi,
I don't know mush about the dx-100 controller but in the dx-200 and YRC1000.
Note: What I type here is for an DX-200 check with your own electric wiring schematics!
The IN/OUT are on CN306 till CN309.
Most external and safety signals you can find on CN219 (board is connected to X18)
It is also possible to program the extern start and servo on through the ladder program.
With SIN#0029 (#40044) and SIN#0030 (40045).