Serial communication
Flow control
Digi XBee® 3 802.15.4 RF Module User Guide
81
For serial communication to occur, you must configure the UART of both devices (the microcontroller
and the XBee 3 802.15.4 RF Module) with compatible settings for the baud rate, parity, start bits, stop
bits, and data bits.
Each data byte consists of a start bit (low), 8 data bits (least significant bit first) and a stop bit (high).
The following diagram illustrates the serial bit pattern of data passing through the device. The
diagram shows UART data packet 0x1F (decimal number 31) as transmitted through the device.
You can configure the UART baud rate, parity, and stop bits settings on the device with the
BD
,
NB
,
and
SB
commands respectively. For more information, see
.
Flow control
The XBee 3 802.15.4 RF Module maintains buffers to collect serial and RF data that it receives. The
serial receive buffer collects incoming serial characters and holds them until the device can process
them. The serial transmit buffer collects the data it receives via the RF link until it transmits that data
out the serial port. The following figure shows the process of device buffers collecting received serial
data.
Use
and
to set flow control.
Clear-to-send (CTS) flow control
If you enable CTS flow control (
), when the serial receive buffer is more
than
FT
bytes 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 less than
FT
bytes in it. See
to configure and read this threshold.
