Pololu TReX User Manual
Page 11
serially to an unpowered microcontroller. Ungrounding the SO pin will cause the TReX to startup as
normal; removing the mix jumper will put the TReX into learning-mode, at which point it will either
start trying to learn the channels or will wait for a valid signal on the input lines. If it waits, it will flash
the red and green LEDs in unison four times faster while waiting.
▪ Red and green LEDs alternate around once per second: The TReX is waiting to see if it should
enter firmware-upgrade mode. This happens when the TReX is in serial mode (i.e. there is no mode
jumper in place), the mix jumper is in place, and the serial out (SO) pin is grounded. This last condition
can arise if the TReX is connected serially to an unpowered microcontroller. Ungrounding the SO pin
will cause the TReX to startup as normal; removing the mix jumper will put the TReX into firmware-
upgrade mode, which will cause the red and green LEDs to start alternating four times faster.
◦ While Running Normally:
▪ Red LED on solid, green LED might flicker: The red LED solidly on indicates that serial is in
control of the motors (i.e. serial override is active or the TReX is in serial mode). While serial is
in control of the motors, the green LED acts as a serial-packet-received indicator. It lights when a
command byte is received and stays lit until the last byte of the command packet is received. The
flicker rate of the green LED will depend on the baud rate you’re using and the rate at which you’re
sending serial commands to the TReX.
▪ Green LED on solid, red LED might flicker: The green LED solidly on indicates that the channel
inputs are in control of the motors (i.e. the TReX is in RC or analog mode and serial override is not
active). While the channel inputs are in control of the motors, the red LED acts as a serial-packet-
received indicator. It lights when a command byte is received and stays lit until the last byte of the
command packet is received. The flicker rate of the red LED will depend on the baud rate you’re using
and the rate at which you’re sending serial commands to the TReX.
▪ Green LED is rapidly flashing, red LED might flicker: The TReX will not let the channel inputs
start controlling the motors until safe-start conditions are first met (see
). Specifically, it is
waiting for a valid signal on all required channels, for the motor signals to request no motor movement,
and for the serial override signal to not be requesting serial override mode. This state occurs when the
TReX first starts running in RC or analog mode, and can be retriggered if an RC signal is ever lost on
a required channel. This state will never occur if the TReX is in serial mode. While in this state, the
red LED acts as a serial-packet-received indicator as described in the bullet point above.
◦ While in Learning Mode (see
▪ Red and green LEDs blinking rapidly in unison: The TReX is in RC mode and it is waiting for a
valid RC signal on at least one channel before it begins learning the channel calibration values.
▪ Red LED on solid, green LED off: This is the first stage of the learning sequence in which the TReX
is attempting to learn the neutral values of each channel. This phase should last around two seconds.
Do not touch the RC/analog sticks while the red LED is on or you could cause learning to fail.
▪ Status LEDs flash rapidly five times: When the TReX is through learning the neutral values, it
will flash the status LEDs five times to indicate which channels had neutrals successfully learned and
which channels failed neutral learning. A green flash indicates success for the corresponding channel;
a red flash indicates failure. If all five channels fail to learn neutral values, the learning process stops,
otherwise it continues to the next phase, which is learning the values of the extremes. Once this
last learning phase is complete, the status LEDs will again flash five times to indicate whether the
corresponding channel was successfully learned. This final five-flash sequence will repeat until the
TReX is reset.
▪ Red and green LEDs both on solid: This is the second and final stage of the learning sequence in
which the TReX is attempting to learn the maximum and minimum values for each channel. This phase
lasts around ten seconds, during which time you should move the control sticks to their extremes.
Make sure to hold each channel at each extreme for at least 0.5 seconds.
Pololu TReX User's Guide
© 2001–2013 Pololu Corporation
3. Getting Started
Page 11 of 24