The CChex_Update funciton in the SDK is the asynchronous data processing. The CChex_Update is use to populate buff with pending messages (such as personnel information, records, etc.) from the device.
When the (CChex_Updat)function returns 0, it just means that there is no message to be processed in pBUFF, and it cannot be used as a loop node. (The device may still be running the called command，do not populate to the BUFF)
The end of the loop needs to manually set the node (such as stop button, etc.)