XBee®/XBee‐PRO® ZB SMT RF Modules
CTS Flow Control
If CTS flow control is enabled (D7 command), when the serial receive buffer is 17 bytes away from being
full, the module de-asserts CTS (sets it high) to signal to the host device to stop sending serial data. CTS is
re-asserted after the serial receive buffer has 34 bytes of space.
RTS Flow Control
If RTS flow control is enabled (D6 command), data in the serial transmit buffer will not be sent out the
DOUT pin as long as RTS is de-asserted (set high). The host device should not de-assert RTS for long
periods of time to avoid filling the serial transmit buffer. If an RF data packet is received, and the serial
transmit buffer does not have enough space for all of the data bytes, the entire RF data packet will be
discarded.
Note: If the XBee is sending data out the UART when RTS is de-asserted (set high), the XBee could send
up to 5 characters out the UART or SPI port after RTS is de-asserted.
Serial Interface Protocols
The XBee modules support both transparent and API (Application Programming Interface) serial interfaces.
Transparent Operation
When operating in transparent mode, the modules act as a serial line replacement. All UART or SPI data
received through the DIN or MOSI pin is queued up for RF transmission. When RF data is received, the data
is sent out through the serial port. The module configuration parameters are configured using the AT
command mode interface. Please note that transparent operation is not provided when using the SPI.
Data is buffered in the serial receive buffer until one of the following causes the data to be packetized and
transmitted:
•No serial characters are received for the amount of time determined by the RO (Packetization Time-
out) parameter. If RO = 0, packetization begins when a character is received.
•The Command Mode Sequence (GT + CC + GT) is received. Any character buffered in the serial
receive buffer before the sequence is transmitted.
•The maximum number of characters that will fit in an RF packet is received.
API Operation
API operation is an alternative to transparent operation. The frame-based API extends the level to which a
host application can interact with the networking capabilities of the module. When in API mode, all data
entering and leaving the module is contained in frames that define operations or events within the module.
Transmit Data Frames (received through the serial port) include:
•RF Transmit Data Frame
•Command Frame (equivalent to AT commands)
Receive Data Frames (sent out the serial port) include:
•RF-received data frame
•Command response
•Event notifications such as reset, associate, disassociate, etc.
The API provides alternative means of configuring modules and routing data at the host application layer. A
host application can send data frames to the module that contain address and payload information instead
of using command mode to modify addresses. The module will send data frames to the application
containing status packets; as well as source, and payload information from received data packets.
The API operation option facilitates many operations such as the examples cited below:
->
->
->
Transmitting data to multiple destinations without entering Command Mode
Receive success/failure status of each transmitted RF packet
Identify the source address of each received packet
© 2010 Digi International, Inc.
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