User Guide

Specification for Spektrum X-Bus Telemetry Sensors
Page 6 Rev E
7 ADDRESSING & DEVICE TYPES
The Appendix includes the telemetry header file used by all Spektrum AirWare-based transmitters. It
defines the device type codes for all Spektrum products and known reserved values. The device type
codes are used as I2C bus addresses by default, but the protocol also provides a means for them to
differ.
Spektrum reserves the right to use addresses not listed as we deem necessary. We do not intend to
interfere with other products, and therefore urge anybody making a device to provide a mechanism to
select different addresses should the need arise. Commercial vendors are urged to contact Spektrum in
order to coordinate addresses and prevent interference.
Note that Spektrum is the owner of all address assignments, and does not guarantee that any unused
address will be available in the future. Only addresses specifically assigned are guaranteed not to
change. Addresses 0x09 and below shall not be used by any third-party devices.
For each of the messages in the header file it should be noted that they begin with the fields identifier
and sID. The identifier field is always under all circumstances an exact match to the I2C address, and
needs to be the first byte of any reply as noted in the hardware-level section. The second byte, sID,
serves as a way to allow either multiple devices of the same type to live on the bus, or for a device to
retain its type code when there is a conflict of the addresses. At this time, none of the AirWare radios
properly display data from multiple instances of the same device type.
Use of the sID field is quite simple:
When sID is zero, then the device type (TELE_DEVICE_xxx) is the same as the bus address identifier.
This is the norm for all Spektrum products. If sID is non-zero, then sID is the device type and
identifier serves only to provide a unique I2C address.
8 DATA FORMATS
All third-party sensors shall report their data in big-endian format (MSB at lower address) if they are to
be displayed on the transmitter screens. All data shall binary 8, 16 or 32 bits. Spektrum uses BCD for
JetCat and GPS but does not support these formats for third-party products.
The TM1100 module notifies the transmitter that it is in use by setting the high bit of the identifier
field. This is informational-only to the transmitter and does not affect operation.
The DSMX Ultra Micro receivers provide Flight Log data only, using the standard QoS record
structure. The receiver voltage field is fixed at 0xFFFF, indicating “no data” to the transmitter.
The transmitter uses two sentinel values to indicate that there is “no data” for a field. For an unsigned
value, a value with all bits set to one (ie, 0xFFFF or 0xFFFFFFFF) indicates this. For a signed value
the “no data” value is denoted by all bits set except the sign bit, i.e. 0x7FFF or 0x7FFFFFFF.
These values and standards are also utilized by post-flight systems to properly display logged data.