Hi Antoine,
Press '?' in the terminal. This will allow you to see the menu for the limited-function ASCII protocol. Keep in mind that none of the protocols are terminated by return, null, or newline.
The legacy protocol supported is prefixed by an ASCII zero '0'. For instance, '09'. You have to write both into the buffer to get a response. The response is an echo of 32-bytes. You would get the reading at the eight offset of the buffer (zero-based counting). In the firmware 0.3.0.0, it is line 149-152 of host_legacy.c.
I take it you understand C? In that case, the firmware is included in the GUI distribution under subfolder "/firmware." If you understand embedded C it should be relatively straightforward to see how all three protocols are supported:
1. legacy (documented in the E2E FAQ), found in host_legacy.c
2. ASCII menu, found in host_interface.c
3. byte-based protocol, found in host_interface.c
We are awaiting approval to roll documentation for all three protocols into the EVM Guide soon.
Thanks,