1. What does EtherCAT stand for?
Ethernet Control and Automation Technology.
EtherCAT is an Ethernet-based industrial automation technology known for its ultra-high speed and excellent real-time performance. It combines the communication advantages of traditional fieldbuses (particularly CAN bus) with the bandwidth benefits of Ethernet, breaking through the communication bottlenecks of traditional fieldbuses. Developed by Beckhoff, it is an international standard and currently the most technically advanced and fastest-growing among all industrial communication protocols promoted. This technology is open with very low development and application costs.
2. What is the major difference between EtherCAT and other industrial Ethernet protocols?
The primary distinction of EtherCAT from other industrial Ethernet protocols is that all communication is handled directly by the hardware of the slave's communication chip. EtherCAT retains its protocol integrity at each slave, where processed data is directly inserted into the respective sub-telegrams within the EtherCAT frame. This data, now logical, can be immediately used by the master through DMA chip replication without further processing. This mechanism results in high efficiency for slaves, as the protocol handling is completely independent of the microcontroller's implementation. It also frees up the master's CPU from data copying and mapping processes, thereby enhancing master efficiency, simplifying slave implementation, and boosting overall system performance, benefiting applications across various fields with EtherCAT communication technology.
3. Some clock concepts in EtherCAT:
- Distributed Clock Mechanism: All slaves are synchronized to a reference clock. The first slave with distributed clock capabilities connected to the master acts as the reference clock, synchronizing other devices and the slave clocks of the master. Precise clock synchronization control requires measuring and calculating data transmission delays, local clock offsets, and compensating for local clock drift.
- System Time - The timing used by the distributed clock.
- Reference Clock - The first slave with distributed clock functionality connected to the master, as defined by the EtherCAT protocol.
- Slave Clock - Clocks of all other slaves except the reference clock.
- Master Clock - The EtherCAT master also has timing capabilities, known as the master clock.
- Local Clock - Each DC slave has its own local clock.
- Initial Offset - At system startup, there's a difference between each slave's local clock and the reference clock, known as the initial offset.
- Clock Drift - Due to each DC slave using its own clock source, there's some drift in their timing cycles, leading to asynchronous clock operation.
- Local System Time - After compensation and synchronization, each DC slave produces its own local system time.
- Transmission Delay - The delay in data frame transmission between slaves, including both internal device and physical connection delays.
Clock Synchronization Principle: Each device's local clock runs freely and will drift from the reference clock. To ensure all devices operate on the same absolute system time, the master calculates the offset between the reference clock and each slave device's clock and writes this into the slaves, allowing them to compute their local system time. This offset enables clock synchronization without altering the freely running local clocks. Clock drift is corrected by the distributed clock mechanism, which self-calibrates based on the comparison between the reference and local clocks.Note: DC stands for Distributed Clock.System time, as we commonly refer to it, is set by the master after distributed clock initialization to the first slave with distributed clock capability, which then becomes the standard for reference clock.
4. Can EtherCAT support parallel network communication like Profinet?
For instance, if an EtherCAT master is connected to 4 slaves and one of the slave's network cables is disconnected, can the other slaves still function normally?
Yes, this can be achieved through:
- Using slaves with rotary switches, like the EK1101, where setting the rotary switch address allows for hot connection.
- Or by employing a star topology, such as with the CU1128, where a disconnection on one line does not affect others.
5. What do K-BUS and E-BUS represent, and what are their differences?
- E-bus refers to the EtherCAT bus.
- K-bus is a high-speed serial bus used for communication between couplers (like CANopen couplers) and modules other than those of the EtherCAT bus.
The key difference is that E-bus is specifically for EtherCAT communication, whereas K-bus is for other types of communication within the system.