By Richard Mourn, Quantum Parametrics LLC



The 1394 (FireWire) audio-video standard has long been popular in computer and consumer electronics applications. I’ve worked on IEEE-1394 since 1992, and almost all of that time was spent focused on consumer electronics products such as camcorders, PC hosts, HDD/DVD systems, digital television, and set top boxes. Now, 1394 is moving into non-CE applications and it's clear that 1394 is an excellent choice for non-traditional multimedia applications.

A few years ago we began to see many innovative implementations of 1394. One interesting one was in the F35 Joint-Strike-Fighter, where 1394 was used in motion control applications to communicate with sensors and actuators. This innovative application led us to understand that if relatively simple devices like these could connect more directly to the 1394 bus without software, we could easily make the devices less complicated -- and less expensive.

We also understood that products in the industrial control market need faster I/O, just like most products in consumer and computer applications. And, while throughput is important, many applications within the industrial control market also require low and/or fixed latency.

Enter VersaPHY, a 100 percent compatible extension to IEEE-1394, which is designed to allow these basic applications to connect to 1394 without the need for device software. The number of devices that benefit is huge. For example, a basic consumer application such as security cameras drives the need for a long haul high bandwidth network such as 1394. With the network established, you get maximum benefit by connecting other devices like security and temperature sensors, doorbells, and lighting controls, among others, all of which can now be easily be connected to 1394 with VersaPHY. The result: reduced wiring costs, along with the ability to provide information and control to the entire audio and/or video network where the devices reside.

Because the 1394 PHY layer has a standardized 8-bit 100MHz interface, the VersaPHY extension can be realized without new silicon. Also, new VersaPHY traffic is ignored by non-VersaPHY 1394 devices/protocols such as IP-1394, camcorders, TV, STB, HDDs, and non-VersaPHY traffic is ignored by VersaPHY devices allowing the two can coexist.

While maintaining compatibility, VersaPHY enabled a few key simplifications to 1394 such as permanent/fixed addressing (device and/or bus configurable); scalable PHY layer addressable registers used to interface directly to the application; and unsolicited responses which enable immediate updates from the device – such as a sensor -- to the controller in a single bus transaction.

1394 node addressing can change based on several factors. This change causes increased complexity for devices and their controllers. VersaPHY’s permanent/fixed addressing allows the simply devices to be configured once - perhaps at installation or manufacture - and then it is always addressed used the same VersaPHY label, or address. Multi-function VersaPHY devices may have unique address space for each function they support. This allows a function view of the network rather than a device view. This also increases the addressable space within an individual node.

1394 PHY registers are read only and only control/report PHY specific functions. The PHY layer addressable VersaPHY registers are defined by the VersaPHY profile (application) and allow the application to directly connect to the PHY.

Unsolicited responses allow the VersaPHY devices to send a response – which is not directly requested by the controller -- to the 1394 bus, by using the permanent node/function address so the controller or other VersaPHY devices can listen in and identify the source of the response. For example, if “sensor A” has a value that changes, it can immediately send an unsolicited response to the 1394 bus. A controller receives the response and -- if it cares about “sensor A” -- it can take action.

Keep in mind that the fixed latency so important for industrial application often if not usually requires point-to-point connectivity. This requirement is easily satisfied by 1394 and VersaPHY, which provide a low and ‘known-worst-case’ latency along with a network wide synchronized clock, which can be used to timestamp events within 20ns of occurrence. This sort of precision is important when trying to provide precise motor control. VersaPHY’s unsolicited response feature allows the simple device (encoder attached to a sensor) to send the sensor data autonomously any time its value changes. The controller simply listens for data and process the data based on the address source of the response.

Also, if the time when the change occurred is important, the 1394-based time stamp -- with 20 nanosecond resolution -- can be appended to the sensor data, and the controller then will know when the event occurred.

Together, 1394b and VersaPHY extend the reach of FireWire beyond the CE and PC markets to become an fully capable industrial network interface that supports Internet Protocol (like Ethernet), inspection cameras, and direct (no software) connection of sensors, actuators and legacy interface devices such as Profibus, Fieldbus, Interbus, Modbus, RS-422/485, I2C, GPIO, and others -- all with the same 1394 network.

It's Simple, and efficient.

For more information about the 1394 (FireWire) standard and its applications, visit Understanding 1394

For information about Quantum Parametrics, visit Quantum

About the Author

Richard Mourn graduated from Kansas State University with a BSEE in 1991 and
began work on P1394 in 1992 at Texas Instruments. While at TI he helped
develop the industries first two production link layer controllers. He
continued working on IEEE-1394 while at NCR along with SCSI and Fiber
Channel. After NCR Mr. Mourn went to Zayante, a 1394 Technology start up,
that was purchased by Apple in 2001. Mr. Mourn co-founded Quantum
Parametrics in April of 2000 a leading provider of IEEE-1394 test services
and VersaPHY technology.