XBee-PRO XSC RF Module operation Serial communications
XBee®-PRO 900HP/XSC RF Modules
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Serial communications
The XBee module interfaces to a host device through a CMOS-level asynchronous serial port. Through
its serial port, the module can communicate with any UART voltage compatible device or through a
level translator to any RS-232/485/422 device.
UART-interfaced data flow
Devices that have a UART interface connect directly through the pins of the XBee module as shown in
the following figure.
The following diagram shows the system data flow in a UART-interfaced environment (Low-asserted
signals distinguished with horizontal line over signal name).
Serial data
Data enters the XBee device through the DI pin as an asynchronous serial signal. When no data is
being transmitted, the signal should idle high.
The UART performs tasks, such as timing and parity checking, that are needed for data
communications. Serial communication consists of two UARTs, one being the XBee device's and the
other being the microcontroller's, configured with compatible parameters (baud rate, parity, start
bits, stop bits, data bits) to have successful communication. Each data packet consists of a start bit
(low), 8 data bits (least significant bit first) and a stop bit (high).
The following figure illustrates the serial bit pattern of data passing through the module. The UART
data packet 0x1F (decimal number “31”) transmits through the XBee-PRO 900HP RF Module example
data format is 8-N-1 (bits - parity - # of stop bits).
Flow control
The following internal data flow diagram shows the five most commonly-used pin signals.
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