Electronic Design

Ethernet Transceiver First To Include IEEE-1588 Precision Time Protocol

By far, Ethernet is the most widely used local-area networking (LAN) technology. More than 90% of all LANs use it in some form, wired by CAT5 or CAT6 or even wireless. Now, the industry is beginning to adopt Ethernet for a wide variety of automation, data-acquisition, test and measurement, and other real-time applications.

Yet one of the biggest problems with Ethernet in industrial applications is the non-deterministic nature of the data transmission. For many applications, Ethernet's Network Time Protocol (NTP) provides adequate timing information if timing resolutions of 10 ms or more are enough. In some cases, though, it's essential to provide a more timely transfer of information for control and monitoring purposes.

The IEEE-1588 Precision Time Protocol (PTP) standard represents a solution to these time-critical problems. For example, it provides time-synchronized motion control to distributed controllers in a manufacturing setting as well as time correlation of data in data-acquisition and test and measurement systems. And now, designers can get a full implementation of IEEE-1588 PTP in National Semiconductor's PHYTER DP83640 Ethernet transceiver.

The IEEE-1588 PTP is a technique for synchronizing the clock signals in one part of a network with clocks distributed throughout the network. One of the clocks is used as a "grandmaster" clock, and all other clocks are considered "slaves" synced to the master clock. This synchronization is accomplished by an exchange of special protocol-specific packets over the network to provide timestamping information.

The timestamping of transmitted and received packets allows designers to determine the difference between clock frequencies and correct for them. The protocol provides a continuous and automatic process where the clock differences are noted and automatically adjusted. This provides timing precision of less than 1 μs and often even less.

The DP83640 is a standard Ethernet 10/100-MHz physical-layer (PHY) transceiver, but it includes all of the hardware to implement the IEEE-1588 time-sync functions (see the figure). The I/O typically is the RJ45 connector to the twisted-pair medium. This chip accommodates the 100BaseFX PHY, which uses fiber, as well.

Also, the DP83640 interfaces to a microcontroller and the Ethernet media access control (MAC) segment of the Ethernet system by way of the standard media independent interface (MII) or the reduced media independent interface (RMII) normally provided. This IC makes a great companion to an embedded controller (or FPGA or ASIC) that doesn't have the IEEE-1588 capability.

The DP83640 comes in a 48-pin low-profile quad flat package (LQFP) and costs $5.24 in 1000-unit quantities. An evaluation board is also available.

National Semiconductor ethernet.national.com

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