Building a low cost deterministic industrial Ethernet system
Industrial Interconnects and Protocol Support
SoC platforms, which include a processor core together with a combination of peripheral interfaces on a single integrated chip, have become widely popular in the standard IT market due to their design efficiency and cost effectiveness.
For an SoC to effectively address the bridging requirements between the disparate network domains of modern industrial or factory automation environments, the integration of several interfaces used to support fieldbus, as well as Ethernet, is required.
An optimal mix would include SPI, I2C, CAN, RS485, TDM, PCI, and Ethernet. In addition to these, the following interfaces and protocols are also recommended to support modern memory and associated peripheral devices: UART (supporting PC16450 and PC16550 programming models), DDR2 SDRAM (with ECC support), USB 2.0, IEEE® 1588 for clock synchronization of networked nodes, and a suitable number of GPIOs - with all pins supporting interrupt capability.
Serial-based fieldbus protocols in use today include PROFIBUS, CAN and DeviceNET. The CAN module utilized in a SoC design should support the version 2.0 specification and be backwards compatible with the previous 1.0 module version.
Industrial Ethernet-based protocols in use include PROFINET, EtherCAT and CANopen. Implementation of IEEE 1588 support for Ethernet should support the version 2.0 specification. The IEEE 1588 protocol enables heterogeneous systems that may include clocks of various inherent precision, resolution and stability to all be synchronized across the network.
A hardware-assisted implementation of IEEE 1588 would support system-wide synchronization accuracy in the sub-microsecond range with minimal network and local clock computing resources. RF connectivity solutions, such as 802.15.4 or ZigBee® technology, should be provided by the PCI controller supporting version 2.3.
Ethernet to Industrial Ethernet/Fieldbus Bridging. A SoC designed with the aforementioned interfaces and features would be able to implement multiple protocols and should support both Master and Slave functionally for each.
Such an SoC could also provide a bridging function between similar or dissimilar protocols. For example, a similar protocol bridging would be from PROFIBUS to PROFINET where only the physical connectivity is changing. A dissimilar protocol bridging example would be where CAN was converted into a PROFINET.
In this case, the conversion would require the complete termination of each protocol to the point where a common mapping of function/telemetry can be achieved. A matrix of possible bridging combinations is shown in Table 1 below.
Table 1: Matrix of Potential Bridging Combinations (To view larger image, click here)
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