5.3 RF Interface
The module integrates a balun filter. The user can connect a 50ohms antenna directly to the
5.4 General Purpose Analog IO
The general purpose analog IOs can be configured as ADC inputs by software. Do not
connect them if not use.
5.5 General Purpose Digital IO
There are nine general purpose digital IOs defined in the module. All these GPIOs can be
configured by software to realize various functions, such as button controls, LED displays
or interrupt signals to host controller, etc. Do not connect them if not use.
5.6 Serial Interfaces
This is a standard UART interface for communicating with other serial devices. The UART
interface provides a simple mechanism for communicating with other serial devices using
the RS232 protocol.
When the module is connected to another digital device,UART_RX and UART_TX
transfer data between the two devices. The remaining two signals, UART_CTS and
UART_RTS, can be used to implement RS232 hardware flow control where both are
active low indicators.
There is a full speed (12M bits/s) USB interface for communicating with other
compatible digital devices. The module acts as a USB peripheral, responding to request
from a master host controller, such as a PC.
The module features an internal USB pull-up resistor. This pulls the USB_DP pin weakly
high when module is ready to enumerate. It signals to the USB master that it is a full
speed (12Mbit/s) USB device. The USB internal pull-up is implemented as a current
source, and is compliant with section7.1.5 of the USB specification v1.2. The internal
pull-up pulls USB_DP high to at least 2.8V when loaded with a 15kΩ ±5%
pull-down resistor (in the hub/host) when VDD =3.1V. This presents a
Thevenin resistance to the host of at least 900Ω. Alternatively, an external 1.5kΩ pull-up
resistor can be placed between a PIO line and DP on the USB cable.