vexctl - Vex robot communication and control utility
vexctl [flags] command [arguments]
Enter "vexctl" with no arguments for a brief list of flags.
command is a utility for communicating with and controlling
the PIC micro-controller in a VEX robot.
is used to perform basic operations such as uploading files,
displaying status information about the controller, etc.
is based on the Robotics Control library (-lroboctl), and is
intended to run on all POSIX compatible platforms. It was developed under
FreeBSD, and is also known to work on Mac OS X and Xubuntu Linux 6.06.
Although the VEX uses an RS232 serial connection to communicate with the
computer, recent VEX kits do not ship with a serial cable. Instead, they
include only a USB to serial adapter to connect with the programming module.
This adapter can be used with Windows, Mac, and any Unix system that supports
the Prolific PL-2303 USB to serial chip.
Depending on your version of FreeBSD, the Prolific device driver may or may not
be built into the kernel. You can find out by running
which will try to load the kernel module. If you get the error "kldload:
can't load uplcom: File exists", then either the module is already
loaded, or the driver is statically built into the kernel.
If the kldload command finishes quietly, this means that the kernel module
loaded successfully. In this case, you should add
to /boot/loader.conf to make it load
automatically when the system is booted. The device /dev/cuaU0 will be created
when the USB cable is plugged in. This is the default device for
For Mac OS X, you must download and install a PL2303 driver (available at the
Prolific WEB site) and reboot. The default device is /dev/cu.usbserial. There
seems to be a glitch with the Mac Prolific driver that causes communication
with the VEX to freeze occasionally. To work around it, simply unplug the USB
cable from your Mac for a moment and plug it back in, so that
/dev/cu.usbserial will be recreated and initialized.
For Xubuntu Linux, the driver is loaded by default, and the default device is
/dev/ttyUSB0. Other Linux systems may require manually loading a kernel
module, and configuring the system to load it at boot time.
For Cygwin, you'll need to install the Prolific driver for Windows, which is
available on the Vex WEB site. With the USB-serial adapter plugged in, check
device manager to verify the COM port assigned to it. The Cygwin TTY device
will be one less than the COM port number, e.g. COM3 in Windows, is /dev/ttyS2
To connect the programming module directly to the serial port on your computer,
you will need a male-female DB9 RS232 extension cable with screws on both
ends. The serial connector on the Vex dongle has posts, and cannot be plugged
into a PC serial port, which also has posts.
Since the default security settings of most Unix systems are fairly restrictive,
it may be necessary to adjust device permissions to allow non root users to
On FreeBSD 5.x and later, this requires altering the devfs
For USB devices, the simplest solution (for those who aren't concerned about the
security of their USB devices) is adding the following lines to
add path 'ugen*' mode 666 group operator
add path 'cuaU*' mode 666 group operator
Also make sure that /etc/rc.conf contains the following
USB device nodes are created according to these rules when the device is plugged
in. Note that these rules make all generic USB devices writable to all users.
Adjust the rules according to your security needs, or use an alternative
strategy such as usbd.conf, or devd.conf.
For static devices (i.e. those created at boot time) on FreeBSD, use chmod to
change the permissions on /dev/cuaa*, and edit /etc/devfs.conf to make the
changes survive the next reboot. For RCX serial devices, the following rules
would do the trick:
perm /dev/cuad0 0666
perm /dev/cuad1 0666
Note again that these rules make all serial devices plugged into com1 and com2
writable to all users. Consider the consequences before setting up such rules.
The Vex robot uses a simple dedicated micro-controller with no operating system,
no display, etc. After a program is successfully uploaded to the Vex
controller, it immediately begins running and has complete control of the
The only communication interface with the robot is through the serial port. Most
Vex programming languages offer some sort of print routine (e.g.
PrintToScreen() in easyC) which sends character strings out the Vex serial
port, presumably to a terminal window on a connected computer. It is often
useful to print information about sensor inputs, etc. to the terminal so that
you can see what the program is doing.
The concept of a terminal comes from the old days of computing when users worked
on large multiuser systems through a keyboard and monitor (a terminal)
connected to the host system through a serial port. Modern graphical computers
use programs that emulate old style terminals. The VEX acts like a simple host
computer sending output and receiving input through the serial port. If your
program produces output (e.g. using PrintToScreen()), it should appear on your
The commercial IFI loaders for Windows have a built-in terminal emulator, which
can optionally be opened after a program is uploaded. In Unix, terminal
emulators tools abound, so you can choose you favorite. You'll need to connect
to the Vex using a serial communication tool from the terminal using the same
serial parameters as the loader. (e.g. /dev/cuaU0, 115200, N, 8, 1). Some
text-based serial communication tools include cu, tip, kermit, and minicom.
Cutecom and seyon are a simple graphical programs that opens up their own
terminal window. If you're running under Cygwin, try Bray++ Terminal, which is
very similar to Cutecom.
/dev/usb*, /dev/ugen*, /etc/devfs.conf, /etc/devfs.rules, /etc/usbd.conf
VEXCTL_DEV - The default device node. Overrides the built-in default,
and can be overridden with --dev flag.
nbc(1), nxc(1), nqc(1), roboctl(3), legoctl(1), ape(1), cu(1), tip(1),
kermit(1), minicom(1), cutecom(1)
Jason W. Bacon