Single-chip solutions have been the holy grail of ZigBee developers. Well, that grail has arrived. Ember's EM250 combines a 16-bit microcontroller (MCU) with the company's 2.4-GHz ZigBee transceiver into a single, low-power chip that fits in a 7- by 7-mm package (see the figure). The single-chip solution shrinks the footprint and bill of materials.
ZigBee targets a range of control and data-acquisition environments. ZigBee networks are designed for a large number of nodes that can automatically construct a mesh network. Such advanced capability isn't required of all ZigBee nodes, though, so most of the network can consist of simpler platforms. Chips like the EM250 are designed for very low-power operation, because battery-operated devices will be the norm.
ZigBee incorporates encryption into its standard, which the EM250 supports using AES-128 and CRC hardware. Ember decided to go with its own 16-bit MCU, making it possible to include a memory-management unit. As a result, the ZigBee protocol stack can reside in its own protected partition. The MCU features the typical set of peripherals, including serial links, general-purpose I/O pins, analog-to-digital converters (ADCs), and timers with pulse-width-modulation (PWM) support. Ample processing and memory headroom lets the Ember ZigBee protocol stack reside in the EM250, leaving well over 50% of the resources available for custom applications.
The company includes an SPI-based Ethernet interface for debugging purposes. This interface also could be used to build a ZigBee-to-Ethernet gateway.
SOFTWARE MAKES IT WORK When was the last time you wrote your own Ethernet sockets protocol stack? Probably never. The same is true for ZigBee. That's why Ember offers a ZigBee protocol stack for the EM250, called EmberZNet. The chip can be bundled with the stack. Of course, you can always roll your own, but why do it?
EmberZNet follows the ZigBee standard but extends its support for advanced debugging and diagnostic support. Additionally, it can perform multihop boot loading, which will be crucial in large ZigBee networks. This also permits upgrades over the air through other ZigBee nodes within a logical mesh network.
Ember's other tools help simplify development and debugging. EmberScope is a graphical, standalone network analysis tool. Ember WorkBench is an Eclipse-based plug-in that also includes a wireless packet sniffer called EmberPeek.
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