Table of Contents
Graupner HoTT Telemetry Protocol
This page provides information about the HoTT protocol and driver implementation.
HoTT Protocol Overview
The HoTT V4 telemetry protocol supports a number of devices/modules:
- Electric Air Module
- General Air Module
- Vario Module
- GPS Module
Communication is half-duplex over a one-wire serial link at 19200 baud and 8N1.
The communications bus supports one master (typically the Graupner HoTT receiver) and multiple slaves (the devices listed above). Each slave is identified by a unique, preset sensor ID.
The master will poll each device in turn, process any response which may or may not be received, and then poll the next device.
Here is a sample poll for an Electric Air Module (sensor ID 0x8e) in binary mode (0x80):
The following example shows a sample response from this module:
7c 8e 00 e0 00 80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f4 01 00 00 19 00 00 00 30 75 78 00 00 00 00 00 00 7d 12
Since each HoTT module provides different functions each also delivers different information and hence data.
Electric Air Module
General Air Module
Timing is critical in making communication work. The basic rules for communication, from the slave device's point of view, are as follows:
- The master will poll for each slave it supports every 200ms and each slave will be polled two times in a row(!).
- Each poll includes a slave device ID. Devices should respond only to polls addressed to them.
- After receiving the poll the slave must wait at least 5ms (max. wait period unknown but up to 6ms seems fine).
- The slave responds by sending one byte at a time with a 3ms delay after each byte (it is rumoured that this can be as little as 0.6ms and is probably OK up to 4ms).