User Manual

drives around. This connector is only required if you want to use your mbed as a USB host; it does not
serve the same function as the mbed’s mini-B USB connector, which is used to program the mbed.
4.i. 3pi Base Pins
The m3pi expansion board has access to a number of pins from the 3pi base via a 20-pin header near
the center of the PCB:
m3pi PCB header for accessing pins on the 3pi
robot base.
Two rows of pins are identical, with columns connected by traces on the underside of the PCB.
Typical users might find this header is useful for accessing power for additional sensors and custom
electronics (see Section 4.b). Advanced users may also find this header useful for accessing the
free or partially free I/O lines of the 3pi base’s AVR microcontroller. If you want to use the 3pi’s
microcontroller as the main controller of the m3pi robot, you can connect your extra electronics to
these I/O lines on the expansion board. If you are using the mbed as your main controller, these I/O
lines will probably not be very useful.
Pins PD0 and PD1 are also free by default on the 3pi (i.e. they are not connected to anything on the
3pi other than AVR I/O pins). These are the 3pi’s hardware serial pins, and the default 3pi firmware
uses these pins to receive commands that tell the 3pi base what to do. These pins connect to serial
lines on the m3pi’s mbed socket and can be connected through jumpers on the m3pi expansion board
directly to the serial pins of a socketed Wixel or XBee wireless module (see Section 4.a). If you want
to use these as general-purpose I/O lines, you can access them through the appropriate mbed socket
pins. Alternatively, you can use your favorite microcontroller board to control your m3pi by routing its
serial pins to PD0 and PD1 through the mbed socket and sending the appropriate serial commands.
The commands for the 3pi’s default serial slave program are documented in section 10.a of the 3pi
user’s guide [https://www.pololu.com/docs/0J21/10.a].
Pololu m3pi User’s Guide © 2001–2017 Pololu Corporation
4. The Expansion Board in Detail Page 36 of 39