From the factory Skaarhoj SDI-GPI-LINK-V1 is configured to control camera IDs 1-8. When input 1-8 is closed to GND, the red tally flag for camera 1-8 respectively will be set on the SDI output from the box. Likewise input 9-16 (on the same DB25 connector) will result in green tally (preview) being set on the SDI output.
If you want tally control of camera IDs other than 1-8 or if you want just red tally for camera 1-16 for instance, you simply configure the inputs in the web interface.
The SDI input should be connected to your source for the camera return feed. This would typically be a program output and possibly enriched with CCU data via either an ATEM switcher, the SKAARHOJ RCP, or the Blackmagic Arduino Shield. The SDI Tally box passes through all CCU information and only overrides Tally information.
Outstanding differences from previous or similar versions
The SDI GPI Link converts 'General purpose inputs' to Blackmagic design tallies over SDI standard