User Guide

Specification for Spektrum X-Bus Telemetry Sensors
Page 5 Rev E
Every device shall be responsible to regulate the supply to a level useful for its operation. The I2C
signals must be 3.3V logic, and the pins in open drain mode so as to not interfere with the logic levels.
In order to maintain compatibility with other products, it is strongly urged that any sensors include two
X-Bus ports to allow them to be daisy-chained in the same manner as Spektrum sensors.
The connector used in the TM1000 and all Spektrum sensors is JST part number S4B-ZR(LF)(SN) or
Digikey part 455-1671-ND.
6 HARDWARE-LEVEL PROTOCOL
The TM1000 is an I2C master device talking at 100kHz to the slaves. For best future compatibility,
devices should support 400kHz as well.
Every device shall reply to a poll with a 16-byte message, the first byte of which is always the polled
I2C address. The remaining bytes are defined in the section on the telemetry header file.
Shortly after the TM1000 starts, it polls all addresses on the bus. During this enumeration phase, the
attached devices must reply with their address as the first byte of the reply. The remainder of the first
message will be discarded by the TM1000, but the full 16-byte message must be available for the
TM1000 to clock in. If a device does not answer the enumeration correctly, the TM1000 will not poll it
any more. It is therefore of utmost importance that the first I2C message be answered correctly. The
TM1000 allows clock stretching per the I2C specification, which allows slow-to-start devices to
enumerate properly in the system. If your device will be slow to start, it is recommended that you first
select a higher address, and second that you use the stretched clock.
The TM1000 transmits data to the ground at a rate of one message per 22ms. The time between polls
for any single device is dependent upon the number of sensors which enumerated on the bus. Note that
the TM1000 reserves two addresses for its internal use, so the maximum rate at which a device is
polled will be no less than 44ms. If timing is a critical function for a particular device, it is necessary
that the device provide its own clock source and not utilize the X-Bus for timing.
Servo Bus +V
Common
SDA
SCL