Pololu Wixel - Manual (Page 34)

Indicator LEDs
The green LED behaves as described in Section 1.a , and also flickers when there is data transferred over USB.
The yellow LED represents the state of the radio. If the Wixel is in a serial mode where the radio is not used, the
yellow LED will be off. Otherwise, the yellow LED turns on and off slowly until radio communication is established
for the first time, after which it blinks briefly once per second and flickers whenever data is sent or received via the
radio.
The red LED indicates errors. The red LED will flash briefly if a byte is received on the UART’s RX line that had to
be discarded because the receive buffers were full. The red LED will turn on when a framing error occurs on the RX
line and will stay on until the RX line goes high.
Control Signals
In addition to relaying bidirectional serial data, this app also relays the values of four control signals: DTR, RTS,
DSR, and CD. The names of these control signals come from the RS-232 protocol, but in this app they do not actually
have the same role as they have in that protocol: they are general purpose digital control signals that can carry any
kind of data that you want them to, as long as that data changes slowly (on the order of 5 Hz or slower) and is limited
to two bits in each direction.
In USB-to-Radio mode, the DTR and RTS signals from USB are transmitted wirelessly to the other Wixel, while the
control signals wirelessly received from the other Wixel are relayed to USB as DSR and CD.
In UART-to-Radio mode, the DSR and CD signals from the digital input pins are transmitted wirelessly to the other
Wixel, while the control signals wirelessly received from the other Wixel are relayed to the DTR and RTS output
pins.
In USB-to-UART mode, the DTR and RTS signals from USB are relayed to the corresponding output pins, while the
values of the DSR and CD input pins are relayed to USB.
If two Wixels are communicating wirelessly with each other and both are in UART-to-Radio mode or both are in
USB-to-Radio mode, then the correspondence between the control lines is as follows: DSR on one Wixel corresponds
to DTR on the other Wixel, while RTS on one Wixel corresponds to CD on the other Wixel.
The default configuration of this app (as shown in the table above) gives the Wixel two inverted output pins (DTR
and RTS), and two inverted input pins (DSR and CD). These pins are inverted, which means that a logical value of 0
corresponds to high voltage (usually 3.3 V), while a logical value of 1 corresponds to 0 V (GND).
By changing the configuration parameters (see below), you can disable these signals, reassign them to different I/O
lines, or add non-inverted inputs and outputs.
Any pin configured as an input will have an internal 20 kΩ pull-up resistor unless it is assigned to P1_0 or P1_1,
which do not have pull-up or pull-down resistors.
You do not have to connect anything to the control signal pins in order to send and receive serial data.
These pins are optional.
General Parameters
• serial_mode: Selects the serial mode (1–3, see list above) or auto-detect serial mode (0). The default is 0.
Pololu Wixel User's Guide © 2001–2014 Pololu Corporation
9. Wixel Apps Page 34 of 64