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Chip offers full and lightweight Zigbee options

Posted: 21 Nov 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Microchip? MRF24J40? Zigbee? 802.15.4? MiWi?

Microchip Technology Inc. has equipped its MRF24J40 device for the 802.15.4 radio chip market with a full Zigbee software offering plus an alternative lightweight "MiWi" (Microchip wireless) protocol that uses only basic join-and-leave operations of the full Zigbee stack. While vendors such as Freescale Semiconductor Inc. and Atmel Corp. have offered simple PHY alternatives to full Zigbee, Microchip is anticipating that designers need a little bit of Layer 2 networking guidance, but might be hesitant to implement a full Zigbee network in some instances.

"If you're thinking of tens or hundreds of thousands of nodes, then the costs of joining the Zigbee Alliance and achieving certification are not a big deal," said Rodger Richey, applications manager for advanced microcontroller architectures at Microchip. "But if you're working with simpler networks with dozens or hundreds of nodes, those costs could be significant. Designers are looking for more than just a simple PHY device, but they don't want a full protocol stack."

MiWi allows developers to create peer, star and mesh topologies using 802.15.4, but without full Zigbee addressing. Microchip will provide the software for free, but said it has no plans to create a multivendor coalition, since costs might then begin to emulate those of the Zigbee Alliance. MiWi is not intended to scale beyond 1,024 nodes?it allows eight coordinators on a network, with up to 127 "children" per coordinator, and a maximum number of four hops per message.

The MRF24J40 is the radio and MAC IC that will implement either protocol. It has a four-wire serial peripheral interface and provides a 20MHz clock reference output that can drive any host MCU of Microchip's PIC or dspPIC class. A 128bit Advanced Encryption Standard crypto engine is embedded in the chip, and modes for in-line or standalone encrypt and decrypt are supported. The chip supports MAC commands for automatic packet retransmission.

Microchip hired RF engineers for its first foray into short-range radio, but also made use of public RF and analog cores in developing the engine. The transceiver offers typical power dissipation of 18mA in receive and 22mA in transmit, dropping to 2?A in sleep mode.

Microchip is offering a full development system with two radio cards with the RF transceiver and PIC18 MCUs, as well as a Zena wireless network analyzer card. Richey called the latter "a critical element" in developing practical wireless personal-area networks. The two system cards in the PICDEM Z development kit are actually a combination of a control-system motherboard and RF daughtercard.

The development kit's list price is $269. The MRF24J40 comes in a 40-pin 6-by-6mm QFN RoHS-compliant package, and is priced at $2.99 each in quantities of 10,000. Full production is slated for December.

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