Compact, low-cost control and sensor networks require a robust framework to address a wide array of applications, from automation to energy management. Echelon's PyxOS is designed to fill the gap between devices such as sensors and switches and higher-level networks like LonWorks and Ethernet.
The PyxOS architecture and chip is a logical tree-structured network with a common controller that manages up to 32 devices (see the figure). The architecture supports a range of physical connections, including a two-wire, ac-coupled system that can also deliver power to devices.
With 20 pins, the chip provides a serial peripheral interface (SPI) or three-wire digital I/O interface. In the latter configuration, a node can connect directly to peripherals like switches or sensors, while the SPI typically connects to a microcontroller. The controller node can act as a gateway to other networks using the SPI. Because each PyxOS chip has a unique identifier, PyxOS clusters can be grouped together into larger networks.
ORGANIZING ONE'S SELF
PyxOS chips are designed to be self-organizing. The PyOS controller automatically manages the structure of the network and keeps track of the addition and removal of PyxOS nodes.
Echelon's Interoperable Self-Installation (ISI) software does more than just supply logical addressing to newly added nodes. It also can provide an association between nodes, even for those accessed through the gateway. An association between a pair of nodes could logically connect a switch and a light.
There are three ways to make this association. First, the vendor can predefine them. With each node possessing a unique ID, it's possible to incorporate a class identifier with a node so a particular chip could be used for, say, the left door lock of an automobile. The second way is to set up the association by program via a host that can identify the nodes involved. Lastly, the PyxOS chip has a switch input. Press the switch on node 1 and then node 2, and the two are associated with each other.
Robust design and low cost are keys to PyxOS's success. The chip should cost between $2 and $3, depending on quantity. Chips can be connected directly to each other, but more often a coupler will be used. The chip type will hinge on the type of electrical connection, such as the polarityinsensitive, ac-coupled version that uses a transformer-based coupler.
Other benefits with PyxOS include simplified wiring and support for almost any topology. Electrical isolation and protection are important in the consumer and industrial environments where PyxOS will be used.
Development kits and application software are available. The PyxOS chip isn't directly programmable, but MCU interfaces and gateways to higher-level networks provide access to the Pyx-OS chip functionality.
PyxOS tries to keep it simple, which is the optimal way to build a large, complex control network.