Dedicated Protocol Gives Distributed Automation Exceptional Realtime Performance

12/19/2002 - PowerDNA – which refers to Distributed, Networked Automation and control – is a system that sets a new industry standard for hard realtime I/O using conventional Ethernet cabling. Developed by United Electronic Industries, the modular system is optimized for realtime control applications requiring both large numbers of analog and digital I/O points in distributed locations as well as extremely fast response. Thanks to the patent-pending DaqBIOS protocol, which transfers commands and data over Ethernet hardware in a deterministic fashion, a PowerDNA system consisting of a PCI/PXI-based controller and multiple distributed nodes with more than 800 mixed analog and digital I/O points can guarantee a response in < 1 msec. A wide selection of I/O configurations is available from the factory.

“We have listened to the voice of the customer and have developed PowerDNA, which will easily meet the needs for distributed hard realtime I/O for the next decade,” comments Shaun Miller, president of UEI. “For several years engineers could purchase Ethernet-based I/O but with insufficient realtime response to address future system requirements. However, our extensive investment in developing the DaqBIOS protocol has solved this problem.”

At the highest level, PowerDNA consists of a Central Controller card that fits into a host PC or PXI/CompactPCI system. To each of its two Ethernet ports users can attach as many as 64 I/O Cubes. Each I/O Cube in turn consists of a metal enclosure that contains a Communications layer, a CPU layer with an embedded realtime kernel, and positions for either three or six I/O layers. Customers select the desired functionality from a range of I/O layers, which are factory installed, configured and calibrated.

Users program their applications in C using a straightforward API that provides access to all hardware functionality. After compiling an application on the host PC, engineers can download it to an I/O Cube in several ways: over the Ethernet, over a serial link or over a USB port. The application can run under host control or as a standalone task.

Each layer in detail
The Central Controller resides in a PC or PXI/CompactPCI system, and it is equipped with a 333-MHz PowerPC processor, 128M bytes of RAM and 256M bytes of CompactFlash memory that stores programs and a mini-OS. The controller offers a pair of 100-BaseT network interfaces, each of which can control as many as 64 I/O modules; a 4-port version of the Central Controller is expected shortly. A controller can run the patent-pending DaqBIOS protocol for guaranteed deterministic performance, but it also supports standard protocols such as TCP/IP that allow users to integrate factory-floor tasks with an enterprise system. As for software, the Central Controller executes QNX or Realtime Linux. And even when supporting hard realtime operation, 80% of the processor’s time is available to run a user application.

Each I/O Cube starts with two core layers. First is a CPU layer, which contains a 66-MHz ColdFire CPU running either ìC/OS or ìClinux plus 16M bytes of SDRAM and 6M bytes of Flash memory (2M bytes for system files, 4M bytes for the user). This layer also provides an IrDA interface so that in the future users will be able to field-configure the CPU module with the assistance of any infrared-equipped PDA running Microsoft’s Pocket PC operating system.

Second, the I/O Cube comes with a Network layer, which provides two RJ45 jacks for daisychaining the Ethernet link to other I/O Cubes; this layer also provides a USB port and a serial port over which users can configure the hardware as well as download new programs or upload process data. Users also daisychain power from cube to cube within this layer. A separate power supply can handle the requirements of three cubes.

The compact unit comes in two models, with either three or six I/O layers, each connecting to the CPU layer over a 32-bit 33-MHz bus with optoisolation so errant field signals cannot disrupt system operation. An I/O Cube with room for three I/O layers measures 4 x 4 x 4 in., while the larger version is 6 x 4 x 4 in.

When configuring an I/O Cube, users can select from several I/O Layers:

Soon to be available is a motion-control layer, while others will supply mass storage and battery operation, making the unit ideal for standalone datalogging or remote/vehicular operation.

The Central Controller communicates through the I/O Cube’s Network layer to individual I/O layers using the patent-pending DaqBIOS protocol. It employs either isosynchronous operation with time sharing, or variable timing in a broadcast scheme, or both. Because the protocol is optimized for process applications, the overhead per message is extremely low and the scheme achieves impressive response times. The system can read all the I/O points on 8 cubes within 1 msec. Thus in that time it can service 2304 digital lines (48 lines/layer x 6 layers/cube x 8 cubes). An analog I/O signal takes more communications bandwidth over the network than does a digital bit, so the number of points the scheme can service in a given time must be adjusted accordingly. A typical application might consist of 800 mixed analog and digital channels in 8 cubes, and again the DaqBIOS protocol can service all of them in < 1 msec.

Price and Availability
The DNA-CC Central Controller with two Ethernet ports lists for $2000. An I/O Cube with the Network and CPU layers along with three open I/O-layer positions costs $895, while an I/O Cube with six open I/O layers sells for $1195. The I/O layers themselves range from $320 (8 digital inputs or outputs) to $1995 (25 high-res temperature inputs).

For further information on this product family and a full datasheet as well as details about the firm’s complete line of data-acquisition and signal-conditioning hardware and software, either call United Electronic Industries at 800-829-4632.

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