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PrintEthernet vs. USB
by Tom Wyatt
Marketing Manager, North America
Some customers have asked why HEIDENHAIN products, like the EIB 74x for example, communicate with a computer via the Ethernet interface instead of the USB interface. The EIB 74x is currently successfully being used in a multitude of applications, and is capable of accepting up to 4 HEIDENHAIN encoders with either 1Vpp incremental (12-bit interpolation) or EnDat 2.1 / 2.2. The output is a standard Ethernet interface using TCP / IP or UDP communication.
There are several technical reasons why HEIDENHAIN chose the Ethernet interface for encoder communication to a computer.
Let's look at the basic data transfer requirements for the EIB 74x:
| Requirements | USB | Ethernet |
| In motion control applications, small data packets must be transmitted with high priority! | Frames can be transmitted every 1 ms | Theoretically not limited, the EIB transmits every 100µs for example |
| Motion control applications may require cable runs as long as 100 meters | <5 meters. Longer lengths are possible with added efforts | 100 meters possible with the proper cable |
| Industrial environments demand good EMC characteristics | EMC stability is typically sufficient for industrial applications | EMC stability is never an issue in industrial applications |
| Use of a standard interface for PC's, Industrial PC's and PLC's | USB is the standard for PC's. However, not necessarily for industrial PC's and PLC's. | Ethernet is supported by most PC systems and PLC's. |
| Connection of the EIB and the PC via different media. (e.g. copper, optical fiber, wireless, etc) | Possible with restrictions | Possible |
USB is definitely the best way to connect consumer electronics to standard PCs at low costs. A PC usually has several USB ports. However, from an industrial motion control point of view, there are requirements for a sturdier and more flexible interface allowing longer cable runs with a faster data transfer rate than USB can offer. Ethernet can meet those demands.