Pololu Wixel User Manual download pdf (Page 5)

Wixel programmable USB wireless

module, bottom view with US

quarter for size reference.

The three GND pins are all connected and are at 0 V by definition. When

connecting the Wixel to other electronic systems, you should make sure that

the Wixel’s GND is connected to the other system’s GND unless you are

doing something very advanced.

The Wixel can be powered from VIN pin. Simply connect a 2.7–6.5 V

power source between VIN and GND, with the positive terminal going to

VIN. It is OK to connect VIN and USB at the same time. See Section 5.a

for more information about powering your Wixels.

The VALT pin is connected to three things: the 5V USB bus power from the

USB port (through a diode), VIN (through a diode), and to the input of the

Wixel’s on-board 3.3 V regulator. The connection to 5V is switched off

when a power supply is connected to VIN. Most people will not need to use

the VALT pin: see Section 5.a for example uses.

The pin labeled 3V3 on the board (3.3V Output in the diagram above) is

connected to the output of the Wixel’s 3.3V regulator. This power source

can be used to power other low-current peripherals in your system. With an

input voltage of 5 V (either from USB, VIN, or VALT), this output can provide up to 150 mA of current. At higher

input voltages, this output can provide up to 100 mA.

The pin labeled RST on the board (RESET in the diagram above) is the reset line of the microcontroller. This pin

can be driven low to perform a hard reset of the Wixel’s microcontroller. This should not be necessary for typical

users, but it can be useful while you are developing a Wixel application (see Section 5.c). This pin is internally pulled

high to 3.3 V, so it is okay to leave it unconnected. If you do wire something to this pin, the CC2511F32 datasheet

recommends adding an external RC filter with values of 1 nF and 2.7 kΩ close to the pin in order to avoid unintended

reset of the microcontroller.

The Wixel has 15 free I/O lines whose behavior depends on the application that is loaded onto the Wixel. Specifically,

these are all of the pins on Port 0 (P0_0 through P0_5), all of the pins on Port 1 (P1_0 through P1_7), and P2_1. The

P2_1 pin is tied to the red LED but the other 14 free I/O lines are only connected to the microcontroller. The P2_2

line is also accessible, but it is tied to the yellow LED and is used to get the Wixel into bootloader mode (see Section

5.c).

The amount of current that can be supplied by the CC2511F32’s I/O pins is not well-documented by the manufacturer.

According to this forum post by a TI Employee [http://e2e.ti.com/support/low_power_rf/f/155/p/31555/319919.aspx], regular

I/O pins are designed to be able to source 4 mA while P1_0 and P1_1 are designed for 20 mA.

Caution: The Wixel’s I/O lines are not 5V tolerant. You must use level-shifters, diodes, or voltage dividers

to connect the Wixel to outputs from 5V systems.

The CC2511F32 has several peripherals that are available to be used in Wixel applications:

• 2 USARTs which can perform asynchronous serial or SPI communication

• 3 timers that are capable of PWM output as shown above, plus 1 more internal timer

• 6 analog input-capable pins, connected to a 7–12 bit ADC

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Pololu Wixel User Manual Page 5