Data Sheet
Table Of Contents
- 1 Design guidelines
- 2 Ordering Information
- 3 Pinout and Terminal Descriptions
- 4 Packaging
- 5 Power control
- 6 Interfaces
- 7 Block diagram
- 8 Example schematics
- 9 802.11 Radio
- 10 Firmware
- 11 Host interfaces
- 12 Electrical characteristics
- 13 RF Characteristics
- 14 Physical dimensions
- 15 Layout guidelines
- 16 Soldering recommendations
- 17 Certifications
- 18 Qualified Antenna Types for WF121-E
Silicon Labs
Page 17 of 45
6 Interfaces
6.1 General Purpose I/O pins
To see which GPIOs are multiplexed with which features, please refer to Table 2.
WF121 contains a number of pads that can be configured to be used as general purpose digital IO’s, analog
inputs or for various built-in functions. Provided functions include a Full Speed USB-OTG port, three I2C-ports,
two SPI-ports, two UART’s, Ethernet MAC with RMII connection and various timer functions. Some of the
pads are 5V tolerant. All GPIO pads can drive currents of up to +/- 25 mA.
Note: In any application, GPIO pins not reserved for a certain function and not driven to some known state by
outside circuitry should be set up as outputs by the application software. Only the Change Notice (CN)
capable pins have pullup capability, and if the rest of the pins are left as inputs, they will be floating at a
voltage between ground and supply voltage, causing increased module power consumption due to leakages.
6.2 Serial ports
Pad number UART 1 UART 2
17 nCTS
19 nRTS
29 TX (output)
32 RX (input)
35 RX
36 TX
44 nCTS (input)
47 nRTS (output)
Table 3: Serial port pads
Two UARTs are provided with RTS/CTS-handshaking. Wired speeds up to 20 Mbps are possible, but the
higher bit rates (above 115200 bps) will require the use of an external crystal on OSC1/OSC2 for sufficient
clock accuracy. The serial ports can also be used as host connections when using an external microcontroller.
To see what other functions are present on the same pins, please refer to Table 2.