Electronic Design

A ZigBee InSight

The Ember Jumpstart Edition for EM260 arrived in a rather large box, for a reason that became apparent once tje box was opened. In addition to the three EM260 development platforms, it included a NetGear 8-port 10/100 Ethernet switch with 4-port POE (Power over Ethernet). The platforms can run off a POE connection, batteries or the supplied power supplies. The network interface makes testing and management much easier but battery operation allows devices to be easily moved around. The kit includes all the hardware and software necessary to start building ZigBee-based applications. The breakout board in the development platform has an Atmel Atmega32L 8-bit AVR microcontroller and uses an EM260 module. It is connected to an Ethernet-based InSight adapter that links the breakout board to an Ethernet network. This allows Ember’s InSight Desktop software to access a node through two routes: wired and wireless. The former is handy for debugging and monitoring purposes making it invaluable during development. Software in the kit includes the InSight Desktop 1.1.4 and the EmberZNet protocol stack. The latter also includes support documentation and sample code. There is also a copy of IAR’s Embedded Workbench for the Atmel AVR with a 30-day license. The protocol stack C code is usable with IAR’s tools. The EM260 The EM260 is a ZigBee transceiver and microcontroller that incorporates the MAC and PHY. It has an SPI interface and its own embedded processor that handles the 802.15.4/ZigBee stack. The host processor (the Atmel AVR on the breakout board) uses the EZSP (EmberZNet Serial Protocol) to interact with the EM260. This type of separation has significant advantages. It provides the maximum headroom on the host and keeps the timing of critical ZigBee functions such as timing within the EM260. The EM260 is flash based so it is possible to update the chip with a newer protocol stack if necessary. The chip has its own battery/power supply monitor. It draws under 1uAin sleep mode and it can wake the processor from a deep sleep. The transceiver is a 2.4GHz IEEE 802.15.4 Compliant unit. It has an integrated transmit/receive switch and a second RF path allowing easy connection to a second, typically external, antenna. It works well in an 802.11b/g environment where we tested the system. It is rated at +3dBm transmit power with an optional +5dBm boost. The chip requires a 24MHz crystal and the on-chip voltage regulator can operate from 2.1V to 3.6V. It comes in a tiny 6mm by 6mm QFN-40 package. The Sign Of Three A lot of things come in threes with this kit starting with three breakout boards, three InSight adapters and cables, three radio communication modules (RCM), three Ethernet cables, three power supplies and three battery pagks. The kit also includes just one Kanda USB programmer. The breakout board has a large patch area and connectors for the InSight adapter and an RS-232 serial interface. Either can be used for diagnostic purposes. There are two undedicated switches and two LEDs that can be accessed by the AVR that is soldered on the breakout board. The AVR and RCM have their own reset buttons. Headers and jumpers provide access and control of all the interface pins of the AVR and the RCM. There is an Atmel ISP header and a JTAG header. The RCM has its own flash programming header that works with the Kanda programmer. The InSight adapter actually has a USB interface and a power input although it can derive power from a POE connection, hence the supplied Ethernet switch. On the other side of the adapter is a pair of connections. One is designed for the breakout board. The other is a direct connection to the EM260 RCM. The three modules are essentially identical but they are programmed for out-of-the-box use as a single sink and two sensor nodes. The InSight adapters are designed for use with a DCHP server. This allowed initial testing once the InSight Desktop was installed. Software Installation The Ember CD contains the Ember stack setup program and an installer for the Eclipse-based InSight Desktop. The latter installs quickly allowing immediate testing once the hardware has been connected to the network. The InSight Desktop is implemented using the Eclipse Rich Client Platform (RCP) (see Eclipse: An Application Framework?. In theory, the Desktop functionality could be incorporated into a standard Eclipse IDE configuration but it tends to be easier to run it as a standalone application especially given the amount of screen real estate it can use. In general, most trace facilities can provide immense amounts of information in real time so the more space the better. It may pay to invest in a wide screen monitor or a dual monitor system. The Desktop can search for the InSight adapters. Once they are located it is easy to track the operation of the network. The wired connection is very handy especially when testing nodes that will have intermittent connections to wireless network. The wired connection let me see packets that were sent but not received. I access to the EM260 via the InSight adapter via Telnet. There is a command line interface that can query and configure the RCM independent of the AVR. The PacketTrace facility also works in this non-intrusive fashion allowing a node to be tracked even as it is controlled by the AVR. Unfortunately, much of the documentation is included with the protocol stack installation that does not add a Windows menu entry like the InSight installation. Still, once I found the index.htm file I was able to find all the other docs. The Quick Start guide and other online documentation from the CD has all the details about the system, the EM260, InSight and the breakout board. Initial startup and testing of the hardware was very quick but things slow down a bit when moving into application development. The IAR installation is easy but linking it to the AVR takes some reading. You can get started programming in an afternoon using some of the demo code but don’t move too quickly. It is a good idea to try reflashing the RCM and AVR just in case you need to do it in the future. Likewise, the IAR installation is relatively independent of the Ember source and support documentation so I had to do a little searching to get started. Overall, it's not difficult; just a little less polished than I would prefer. It is a minor hurdle and of little consequence once some applications are under your belt. One advantage of the system is the ability to download code to the RCM and AVR via Zigbee. This is not a major issue with only three nodes but it is invaluable in larger networks and something I was able to try out once everything was up and running. The InSight Desktop provides this support. Developers should have an easy time working with the EM260 given its EZSP C API. The functions tend to be at a higher level than most ZigBee stacks. It is still possible to use the ZigBee API. The latest version support ZigBee Device Objects but I had an earlier version that did not have this advanced support. The only complaint I have about the overall package is the minimal coverage with respect to application development on the AVR. While many will be using other microcontrollers with the EM260, and the docs do address this, the kit should have more description and demos highlighting the Ember stack. One thing I have not yet addressed is the quality of the Ember stack. In a word, it’s great. Ember tends to be on the cutting edge with its ZigBee support and the InSight tools are first rate. The Ember stack handles all the various configurations including the more complex mesh environment. The advantage of the EM260 is that most of this complexity is hidden from the developer. This includes the ability to download applications and to monitor the health of the network. Related Links Eclipse Ember

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