Reverse Engineering the Hub to Hub Word Blocks of the LEGO MINDSTORMS Robot Inventor (51515)
The hub to hub communication blocks exploit the Bluetooth Low Energy (BLE) capabilities of the MINDSTORMS Hubs
The protocol is based on broadcasting data in the advertisement data similar to Beacons.
When transmitting data using the wordblock: 
the hub starts advertising the following data
0x0C, 0xFF, 0x97, 0x03, 0x01, 0x1D, 0xC6, 0x73, 0x49, 0x61, 0x62, 0x63, 0x64
^ ^ ^ ^ ^ ^ ^ ^ ^ ^
| | |_____| | |_________________| |_________________
| | | | | ASCII string containing transmitted data (number of bytes depends on the length of the transmitted data, the maximum is 23 bytes)
| | | | Signal name encoded as a CRC32 hash
| | | Index of the message
| | LEGO Company identifier
| Indicating manufacturer data
Length (number of bytes that follow, not including this one)