Operation
Force UART operation
XBee 868LP RF Modules User Guide
75
Note
Serial port flow control is not possible when using the SPI port.
CTS flow control
If you enable CTS flow control (
D7
command), when the serial receive buffer is 17 bytes away from
being full, the device de-asserts CTS (sets it high) to signal to the host device to stop sending serial
data. The device reasserts CTS after the serial receive buffer has 34 bytes of space. See
for the buffer size.
In either case, CTS is not re-asserted until the serial receive buffer has
FT
-17 or less bytes in use.
RTS flow control
If you send the
D6
command to enable RTS flow control, the device does not send data in the serial
transmit buffer out the DOUT pin as long as RTS is de-asserted (set high). Do not de-assert RTS for
long periods of time or the serial transmit buffer will fill. If the device receives an RF data packet and
the serial transmit buffer does not have enough space for all of the data bytes, it discards the entire
RF data packet.
The UART Data Present Indicator is a useful feature when using RTS flow control. When enabled, the
DIO19 line asserts (low asserted) when UART data is queued to be transmitted from the device. For
more information, see
.
If the device sends data out the UART when RTS is de-asserted (set high) the device could send up to
five characters out the UART port after RTS is de-asserted.
Force UART operation
Condition
You configure a device with only the SPI enabled and no SPI master is available to access the SPI slave
port
Solution
Use the following steps to recover the device to UART operation:
1. Hold the DIN/CONFIG low at reset time.
2. DIN/CONFIG forces a default configuration on the UART at 9600 baud and brings up the device
in Command Mode on the UART port.
You can send the appropriate commands to the device to configure it for UART operation.
3. If you write these parameters to the device, the module comes up with the UART enabled on
the next reset.
Serial interface protocols
The XBee 868LP RF Module supports both Transparent and Application Programming Interface (API)
serial interfaces.
