Digi XBee SX 868 - SPI Operation

Operation Serial communications
XBee® SX 868 RF Module User Guide
53
Signal Function
(SlaveSelect)
SPI_ATTN (Attention) Alerts the master that slave has data queued to send. The XBee SX 868 RF
Module asserts this pin as soon as data is available to send to the SPI
master and it remains asserted until the SPI master has clocked out all
available data.
In this mode:
n
Data is most significant bit (MSB) first.
n
Frame Format mode 0 is used. This means CPOL= 0 (idle clock is low) and CPHA = 0 (data is
sampled on the clock’s leading edge).
n
The SPI port only supports API Mode (AP = 1).
The following diagram shows the frame format mode 0 for SPI communications.
SPI operation
This section specifies how SPI is implemented on the device, what the SPI signals are, and how full
duplex operations work.
SPI implementation
The XBee SX 868 RF Module operates as a SPI slave only. This means an external master provides the
clock and decides when to send data. The XBee SX 868 RF Module supports an external clock rate of
up to 6 Mhz (6 Mb/s).
The device transmits and receives data with the most significant bit first using SPI mode 0. This means
the CPOL and CPHA are both 0. We chose Mode 0 because it is the typical default for most
microcontrollers and simplifies configuring the master.
SPI signals
The XBee SX 868 RF Module supports SPI communications in slave mode. Slave mode receives the
clock signal and data from the master and returns data to the master. The SPI port uses the following
signals on the device: