Endstop don't work, when more than one endstop are connected

Hi everyone,

The electronic I use is the Sanguinololu, I have here one problem with the endstop.

The endstops will not work, when several endstops are connected on the Sanguinololu.

I tried to connect them separate, only connected one of them on the X or Y or Z axis.It works. So the hardware of the endstops are in function.
But when I connect 2 endstops on the X and Y axis. They will not work. I can't stop X or Y motor with pushing the endstops.

What is the solution of this problem?
Thanks all.

Hi everyone,

I found out the reason. With Sanguinololu are on resisters for endstops required.
That is the problem.