ENGINEERING FEATURE

The Exciting Potential of Wireless Communication

With references to example parts, this Arrow Innovation article looks at the increasingly important ZigBee and IEEE 802.15.4 wireless communication components carried by Arrow that enable companies to develop low cost consumer, medical, industrial and many other low power, low data rate communications-based applications.



ZigBee^TM is the name given by the ZigBee Alliance group to the high level communication protocols based on a specification developed by the IEEE 802.15.4 task group for systems controlled by a network of wireless switches and sensors.

A Standard Advantage

The benefit of recognised standards like IEEE 802.15.4 and ZigBee is the promise that designers can mix and match components or devices to build ‘best-of-breed’, or least-cost, products. In practice, the need to ensure all parts are fully compatible, the advantage of directing technical queries and fault reports to a single supplier and – equally important – the time and cost saved on isolating faults to a particular part and supplier tends to favour single-supplier sourcing.

ZigBee or IEEE 802.15.4

IEEE 802.15.4 is a simple protocol for packet data and specifies the MAC (Media Access Control) and PHY (physical layer) networking layers. ZigBee adds security, a logical network, application software and provides networking structures, static and dynamic star, cluster tree and mesh, that allow network coverage over a large area, scalable networks and single point-of-failure avoidance. Designers can build devices based on the IEEE standard or ZigBee that deliver data rates of 250Kbps and 20Kbs respectively over short distances (from 10m to 75m) within one of three wavebands, 2.4GHz (channels 11 to 26 at 250Kbps) international, 868MHz Europe (channel 0 at 20Kbps) and 900MHz US (channel 1 to 11 at 40Kbps).


Figure 1: ZigBee Stack, courtesy of NEC

ZigBee differs from other wireless technologies in enabling networks that can run for many years on inexpensive stand-alone batteries, making them viable alternatives to hard-wired systems. It is especially suited to remote control and sensor applications in harsh radio environments and isolated locations or to building low cost, low power and low data rate devices.

Transceivers - the Fundamental Components

First we shall look at a fundamental component of a ZigBee or 802.15.4 application, the transceiver, and take Atmel’s AT86RF230 low power, high sensitivity 2.4 GHz transceiver as a good example. The AT86RF230 is a low cost SPI (System Packet Interface)-to-antenna with most RF-critical components apart from the antenna, crystal and de-coupling capacitors integrated on chip. It boasts -100dB receive sensitivity and 3dB transmit power and a line-of-site range that Atmel says is up to 2.8 times better than competing radios, reducing the number of nodes required in the network and cutting system cost by as much as 60%.

Atmel also offers a family of 8-bit RISC microcontrollers (MCUs) with a suite of easy-to-use tools and Flash memory densities ranging from 32KB to 256KB, enabling secure, fast and cost-effective remote upgrades. An RF accessory kit, RZ502, enables point-to-point links development, debugging and demonstration. By combining Atmel’s radio and microcontroller parts with some of the world’s best wireless software companies, Atmel provides a near single-source solution for many wireless applications.


Figure 2: Atmel Development System

One Stop Shops

Freescale also aims to supply a one stop shop for ZigBee and IEEE 802.15.4 devices that includes RF transceivers, MCUs, sensors, MAC software, Z-Stack^TM ZigBee software and a development tool set. The MC1320x is its next-generation family of 802.15.4 compliant radios whose enhanced features include an integrated Tx/Rx switch and a reduced external component count that reduces the bill of materials (BOM) and development cost. These radios support Freescale’s Simple MAC (SMAC), the 802.15.4 MAC and the full ZigBee stack option.


Figure 3: Freescale MC1321x block diagram for sensor applications

Systems on Chip Cut BoM

The MC1321x is a System in Package (SiP) series integrating the MC9S08GT MCU with the MC1320x transceiver in a single 9mm x 9mm LGA package and three memory configurations ranging from 16KB to 60KB Flash memory.


Figure 4: STMicrolectronics SN250 Block Diagram

STMicroelectronics also offers a single chip solution, the SN250, with integrated transceiver, 5dBm power increase in Boost mode transmission and Boost mode receiver sensitivity in of -98dBm. A flexible antenna interface enables easy antenna connection with or without an external power amplifier. The power-efficient 16-bit RISC processor includes 128KB of embedded Flash and 5KB SRAM plus a hardware encryption engine (AES 128) with true random number generators.

The newer SN260 is a network processor chip that enables designers to implement their preferred microcontroller to run the applications while the SN260 provides the ZigBee functionality. This allows companies to build ZigBee-enabled applications more quickly using tools with which they are familiar.

Texas Instruments offers the CC2420, a low cost single chip 2.4 GHz IEEE 802.15.4 compliant RF transceiver designed for low voltage, low power applications. In a typical application, the CC2420 will be used together with a microcontroller and a few external passive components. It includes a digital, direct sequence, spread spectrum baseband modem providing a spreading gain of 9dB and an effective data rate of 250kbps. It provides extensive hardware support for packet handling, data buffering, burst transmissions, data encryption, data authentication, clear channel assessment, link quality indication and packet timing information.


Figure 5: Texas Instruments' CC2420 2.4 GHz transceiver

These features allow the CC2420 to interface low cost microcontrollers. The configuration interface and transmit/receive FIFOs of CC2420 are accessed via an SPI interface. CC2420 is based on Chipcon’s SmartRF®03 technology in 0.18µm CMOS.

Texas Instruments is also currently offering unqualified prototypes of a System on Chip (SoC) solution for 2.4GHz. The CC2430 comes in three different versions with 32KB, 64KB or 128KB Flash memory, the excellent performance of the leading CC2420 RF transceiver, an industry standard enhanced 8051 MCU, 8KB RAM with 4KB data retention and other powerful features. The CC2430 will suit ultra low power applications that need excellent receiver sensitivity and robustness to interference.

For customers wishing to know more about the Texas Instruments range, please note that Arrow Electronics UK is holding free one-day technical workshops in April based around the Texas Instruments low power radio products, tools and techniques. Registration is necessary before 1 April; more details on this and other events from http://www.arrowne.com/seminars_events/ti_chipcon/index.shtml then click on the event in which you are interested.

Evaluations Boards, Development Platforms and Application Ready

Evaluation boards and application ready development platforms are available from a number of suppliers and several extended versions are under development for delivery later this year.

Renesas offers a platform for product developers at 2.4GHz with a 900MHz system currently in development. The RZB-CC16C-ZDK is the first of three kits in Renesas' development environment. It includes the hardware, software and documentation necessary to experience true ZigBee networking capabilities first hand.

The kit consists of four M16C 2.4 GHz RF development boards with one board pre-programmed with sniffer functionality (additional boards can be ordered to expand the network) and a full implementation demo version of the in-house developed ZigBee stack and IEEE 802.15.4 MAC software. The packet sniffer can follow devices as they create and join networks and trace packets transmitted over the air between nodes. Also included is an evaluation version of the M16C software development tool set for developing M16C applications. The 900 MHz Solution will offer the same features when available.


Figure 6: Renesas’ RZB-ZMD16C-ZDK ZigBee Demonstration Kit

NEC Electronics expects to deliver its TK-850/SG2+UZ development platform this month; this is an IEEE 802.15.4 compliant ZigBee-Ethernet Gateway with web server, V850ES/SG2 32-bit CPU, 384KB Flash, 32KB RAM, UZ2400 transceiver, Flash programming and debugging via USB connection to PC. It comes with a bundled compiler (128KB max), debugger, TCP/IP, HTTP, SMTP, POP3 and IEEE 802.15.4 MAC stack library. With the ZigBeeSDK, available separately, it enables peer-to-peer mesh networking compliant with the Enhanced ZigBee standard. The table below compares NEC’s products.

NEC Electronics ZigBee/802.15.4 product range

	TK-850/SG2+UZ	TK-78K0/KF2+UZ	78K0 UZ Stick
Microcontroller	V850ES/SG2 UPD70F3281YGC 384KB Flash EEPROM 32KB RAM	78K0/KF2 UPD78F0547DGK 128KB Flash EEPROM 7KB RAM	78K0/KE2 UPD78F0537DGA 128KB Flash EEPROM 7KB RAM
CPU Clock	20MHz	16MHz	16MHz
Power supply	4 x AA batteries, or USB power	006P battery, or USB power	006P battery, or USB power
Ethernet I/F	one channel	None	None
LED	1 each for Power, LAN, and LINK, and 4 for Application	1 for Power, and 3 for Application	1 for Power, and 3 for Application
Tact switch	1 for Reset, and 2 for Application	1 for Reset, and 3 for Application	None

IEEE802.15.4 provides the means to implement a wide range of applications where the scalability and additional coverage of ZigBee are unnecessary. Where wide area coverage, scalability and avoidance of single points of failure are relevant, ZigBee is the right candidate. When considering whether to adopt the technology, however, developers need to be aware that other solutions are sometimes possible and may be less costly, especially when including in the implementation costs the fees for IEEE certification and buying MAC addresses.

Arrow Northern Europe carries a wide range of RF and communication solutions suited to most environments and applications giving engineers the freedom always to choose the best technology and components for their designs.

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