SI4468-7 Datasheet, PDF (45/57 Pages) Silicon Laboratories – Highly configurable packet handler

Si4468/7
9.3. IEEE 802.15.4 Support
Si4468/7 supports the mandatory features of MR-FSK PHY specified in IEEE 802.15.4g as well as some key
features from IEEE 802.15.4. The high level of integration makes it easy to use and offloads the host
microcontroller from these tasks. To support the 802.15.4 MAC, the device has a specific 802.15.4 boot mode. In
this mode, the device only processes 802.15.4 / 4g packets and no customization is possible at the packet level.
This mode is supported by an 802.15.4 stack running on a Silicon Labs MCU or SoC. In this mode, the device only
supports the packet format defined in the 802.15.4 standard. There is no flexibility to support non-802.15.4 packet
formats in this boot mode. Custom packets, including those based on the 802.15.4g PHY standard, are fully
supported in the EZRadioPRO boot mode.
802.15.4g PHY modes including CRC handling and dual sync word are supported in the PRO boot mode as well.
The key features are described below.
9.3.1. CCA Functionality
Basic clear channel assessment (CCA) functionality is supported in any boot mode and relies on RSSI being
above or below a user defined threshold. In addition, the chip supports CSMA / CA and Energy Detection (ED) as
defined in IEEE 802.15.4.
9.3.2. CSMA/CA
The carrier sense feature is fully supported in the 802.15.4 boot mode of the device and is specific to the 802.15.4
packet format. Support for CSMA/CA in the EZRadioPRO boot mode requires host microcontroller support to
implement the back-off timer.
The device can send an IEEE 802.15.4 packet with a CSMA/CA algorithm before the packet and reception of an
ACK packet afterwards without host interaction. The host loads the IEEE 802.15.4 packet into the TX FIFO via the
WRITE_TX_FIFO command.
The CSMA/CA algorithm must pass before sending the packet
If configured, the transceiver will listen for an ACK after successful transmission of the packet
The CSMA/CA algorithm listens on the transmit channel to see if the channel is clear before transmitting the
packet. The period in which the transceiver listens is defined in units of symbols. If the RSSI measured is greater
than a user-defined threshold, the transceiver deems that the channel is busy and does a backoff for a random
amount of time up to five backoff periods. The units of the backoff are defined in symbol times. If the channel is
clear during the listening period, then the transceiver will proceed to transmit the IEEE 802.15.4 packet. If the
transceiver exhausts all of the backoff periods, the transceiver will post a TX_ERROR interrupt with a
TX_ERROR_STATUS of CCA_FAIL.
Below is an example of a transmit operation where the first CSMA check fails and the second one passes.
Rev 1.0
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