What is the standard used by Zigbee networks? Describe its characteristics.

Zigbee What is it?

In the wireless world, the terms Bluetooth and WIFI have become a household names in recent years. They find wide acceptance in applications using mobile sensors.

Zigbee is born out of huge demand arising from industry and others for wireless DAS (Data acquiition system) applications that use lower data rate, longer battery life, simpler design and low cost solutions.

Zigbee Applications
Zigbee technology is based on IEEE 802.15.4 industry standard. . It supports all network topologies namely STAR, MESH and CLUSTER tree. project Developers need only have to focus on application while the hard ware and networking parts are taken care off.

There are 3 types data collection methods used by Zigbee networks.
a Data on demand
An example of this traffic is a wireless sensor to read the water meter. The sensor is programmed to wake up at certain interval to transmit the information needed and goes back to sleep after this is done.

b) Asychronous data
An example of this traffic is a wireless light switch operation. Here command circuit is triggered by external input and wakes up on receipt of the message from master controller . When action is over, it is local unit is disconnected from the network and hence saves energy.

c) Repetitive data
An example of this traffic is security monitoring.Time multiplexed monitoring devices are to return their status to the network. This type use consumes more energy.

Popular Zigbee applications include metering gas/water/electricity readings. Here readings are automatically send to utility headquarters for further action. This saves time and money. In the area of warehousing/inventory management , the wireless technology will enable accurate and hassle free management of goods. Security and access control, and lighting control are other applications that can be implemented with ease.Home automation system to control lightings, blinds, air conditioning, security system, remote control and appliances can be implemented eassily.


IEEE 802.15.4 standard

IEEE 802.15.4 is a simple standard that specifies the Media Access Control (MAC) and Physical (PHY) networking layers for packet data protocol. Its license free frequency bands are:

2.4 GHz (16 channels with baud rate of 250 kps)
902 MHz - 928 MHz (10 channels with baud rate of 40 kps)
868 MHz - 870 MHz (1 channel with baud rate of 20 kps)

North America, Europe, Australia and New Zealand use the sub 1 GHz bands whereas the rest of the world uses 2.4 GHz bands.

It uses Carrier Sense Multiple Access with Collison Avoidance for Channel Access.

The security method used is AES-128.

Has message acknowledgement and a host of other features.

Field programmable gate arrays (FPGA )

Field programmable gate arrays(FPGA) are advanced programmable logic devices. The word field in the name signifies the ability of the gate arrays to get programmed by the users. The word array indicates that series of columns and rows of gates that can be programmed by the end user.
As compared to standard programmable gate arrays , FPGAs are larger devices. The basic cell structure of FPGA is more complex than that of other standard Programmable devices .In FPGA these are known as configurable logic blocks (CLBs).
The FPGA architecture uses three types of configurable elements. the perimeter input/ output blocks (IOBs) , a core array of configurable logic blocks (CLBs) and resources for interconnection. The IOBs provide a programmable interface between internal array of logic blocks and device's external pins. CLBs perform user specific logic functions. And the interconnect resources carry signals among the blocks.
A configuration program stored in internal static memory cells determines the logic functions and their interconnections. The configuration data is loaded in to the device during power up reprogramming functions. FPGA devices are customized by loading configuration data in to the internal memory cells. FPGA device can either actively read its configuration data out of an external serial/ parallel PROM ( master mode ), or configuration can be written to the FPGA device (slave or peripheral modes)

PLA & PAL devices

Describe PLA & PAL in detail?

PLA is a device with programmable AND array and programmable OR array. However in PAL, the programmable array logic is a fixed OR array and a programmable AND array. Because only AND array is programmable, the PAL is easy to program. But it is less flexible than PLA.

Some PALs have flip-flops at the output. The flip-flops store the outputs. Together these flip-flops can serve as a register. Generally, these flip-flops have tristate buffers, hence the output of the registers can easily be controlled. The flip-flop outputs are made available as input to be used in generation of additional product terms. This feedback feature allows PALs to be used for design of counters, registers and sequential controllers.

Programmble logic array

1. what are the various types ICs used in fabricating digital functional blocks?
Fixed function ICS
Application specific ICs
Field programmable ICs

2. Describe how a PLA functions? Compare PROMs and PLAs
The working principles of PROMs and PLAs are similar.However PLAs does not provide full decoding of input variables and does not generate all miniterms as in a PROM.A PLA uses a group of AND gates in place of address decoder, each input of which can be programmed to generate a product term of input variables.