User's Manual Part 2

Software Design
Wireless Sensing Triple Axis Reference design, Rev. 0.9
38 Freescale Semiconductor
5.3 ZSTAR RF protocol
The ZSTAR demo uses very simple protocol to transfer the accelerometer, button and calibration data
between the Sensor Board and the USB stick over the RF medium. The protocol is built on top of
SMAC
(Simple Media Access Controller)
drivers that are available for the MC13191 transceivers family. The
protocol is bidirectional allowing the set up of independent connections amongst numerous pairs of
ZSTAR demos.
All data is transferred in so-called Zpackets. This protocol is primarily targeted at simple demo purposes,
allowing a fast transfer of the accelerometer data in short packets with minimum overheads and with
minimum battery loads (most of the receive windows eliminated, short transmit packets, etc.).
5.3.1 Zpacket format
The ZSTAR Zpacket is contained inside the MC13191 standard packet structure, which is consistent with
the IEEE 802.15.4 Standard. The SMAC library transparently adds a 16 bit Packet control field (see
chapter 7.2.1.1 of IEEE 802.15.4 Standard specifications) to differentiate packets from ZigBee and other
standards.
The Zpacket becomes a payload data for the SMAC standard packet and contains the following fields:
•
Network number
• RX strength
• Zcommand
• Zdata
Figure 5-1Zpacket format
Preamble SFD FLI
Payload Data
FCS
MC13191 Packet Structure
SFD (Start of Frame Delimiter)
FLI (Frame Length Indicator)
FCS (Frame Check Sequence)
Network number
RX
strength
Zcommand Zdata
ZSTAR Zpacket Structure
Packet control
SMAC payload
SMAC Packet Structure
field