Solution:

The limit switch function 'EL+', 'EL-' is used to protect machine when the motor is running. The PCL-839 will stop motor automatically when receive the signal. You don't need to write any code to enable it. All you have to take care is the wiring. The way of wiring should match the setting of JP1, JP2, and JP3. Please refer to manual pg.10 for limit switch wiring. Regard to ORG, SD+, and SD-, before using it, you should enable it by setting operation mode (manual pg.64), and the wiring are the same with EL+, EL-. To see how the limit switch work, you take use of the 'Manual.exe' file. First, set the JP1, JP2, and JP3 on the 'LO' position and connect stepping motor to CHA and connect LCOM of CHA (CN3-pin12) to 5V. Then execute Manual.exe and press 'Ctrl' + '->' and you will see the motor start rotating. Now connect ORG of CHA (CN3-pin30) to GND, and you can find the motor stop immediately. If you connect 'EL+' or 'EL-' to GND, the motor will not rotate at all. You can verify whether the card and the wiring is OK by 'Manual.exe'.