Hello,
JazzCNC and Doddy provide with right pieces of advice!
The LTP port doesn't contain an optocoupler.
It is better to connect a BOB with optical isolation.
For example, PLC4x-G2(please see its English manual https://purelogic.ru/data/docs/elekt..._manual_en.pdf )
Also please see the new English manual for PLCM-E4 http://pumotix.com/upload/iblock/26a...30004d074b.pdf
please keep in mind that having such a controller, you can get basic features of our software http://pumotix.com/ .