If you are referring to API mode it is described in the manual here: https://www.digi.com/resources/documentation/Digidocs/90002258/#Containers/cont_api_mode.htm%3FTocPath%3DOperate%2520in%2520API%2520mode|_____0
Here is a description of all the api frames you can send:
https://www.digi.com/resources/documentation/Digidocs/90002258/#Containers/cont_frame_descriptions.htm%3FTocPath%3DAPI%2520frames|_____0
XCTU has a nifty tool that lets you construct frames and help visualize their format. I would recommend these resources.
Good luck!