TReX’s RX or SI line should connect to your target’s transmit line (the orange wire in the figure above). On a DB9
connector, pin 2 is your computer’s receive line and pin 3 is your computer’s transmit line.
Warning:
It is very important that you do not connect your TReX’s TTL pins (SO and SI) to an RS-232
port. RS-232 serial communication signals range from -12 to +12 V, which is well outside the 0 – 5 V
expected on those lines. Only the COM pins (TX and RX) are designed to handle RS-232 voltages.
3.c. Jumper Settings
The TReX comes with four blue shorting blocks as shown in the picture below. These jumpers let you affect some
aspects of its behavior without serial configuration commands. Note that we recommend you always power off your
TReX before changing jumpers (other than the mix jumper, which can be changed at an time). This is not strictly
necessary, but it is the safest practice.
TReX jumpers
•
Channel-Mix (a.k.a. Single-Stick) Jumper:
When this jumper is in place, the TReX operates in single-stick
mode. Channel 1 is treated as turn left/right while channel 2 is treated as forward/reverse. When this jumper
is off, channel 1 directly controls motor 1 and channel 2 directly controls motor 2. This jumper may be added
or removed on the fly.
•
Battery Elimination Circuit (BEC, a.k.a. +=Vcc) Jumper:
When this jumper is in place, the middle
column of channel input pins is connected to Vcc (5 V). You can use this jumper to power your RC receiver
or analog controller through your TReX. If your RC receiver is powered via another source, you must leave
this jumper off.
Warning:
The Vcc column is tied to the output of a linear voltage regulator, so its current output is
limited by thermal dissipation. The regulator will only be able to safely supply a maximum of 100 mA
when VIN is 16 V (it has a 1-W power dissipation rating). This is typically sufficient for powering an
analog joystick or RC receiver, but it is insufficient for powering servos. If you want to connect servos to
some of your RC receiver channels, you must power your RC receiver separately and disconnect the BEC
jumper. Attempting to use the TReX’s regulated Vcc line to power servos can permanently damage the
TReX.
•
Mode-Select Jumper:
This jumper specifies the interface that is in control of the TReX. When it shorts the
left two pins (as shown in the jumper image above), the TReX is in RC mode, which means the TReX is
expecting RC pulse inputs on its five input channels and that these RC signals will determine the motor
Pololu TReX User's Guide
© 2001–2009 Pololu Corporation
3. Getting Started
Page 7 of 22
