As of mid 2016, RED have changed their Run/Stop input trigger circuitry: RED cameras now employ the "Momentary Ground" technique, the same as camera manufacturers like ARRI.
This circuitry is now located in DSMC2 modules - not the brain. Note that the Base Expander uses the old technique (3v3 Schmitt Trigger), whereas all other DSCM2 modules use the 'new' Momentary Ground trigger.
All RTMotion kits should be able to trigger both methods. Latitude uses the same camera cable for both DSMC and DSMC2 cameras.
MK3.1 receiver you will need to order a specific DSMC2 cable that we now have shipping. http://www.rtmotion.com/products/red-dsmc2
In addition to this please make sure;
1. You have the correct camera selected in the menu of the MK3.1 Controller.
2. You have changed your serial communications setting on the camera to RCP (Redlink Command Protocol) You can do this via;
SETTINGS - SETUP - COMMS - SERIAL - RCP (DSMC)
SETTINGS - COMMS - SERIAL - RCP (DSMC2)