Common encoder protocol

SSI communication protocol

SSI communication protocol is abbreviated, and its full name is synchronous serial interface. The frame format of SSI communication is shown in Figure 1. The data transmission adopts synchronous mode. When data transmission does not occur in the idle stage, the clock and data maintain high potential. The encoder is triggered to load and send data at the falling edge of the first pulse, and then the encoder sends data at the rising edge of each clock pulse. The high bit of the data is in the front and the low bit is in the back, When all bits are transmitted, the clock returns to the high level and the data is correct

It should return to high level

T is the pulse frequency of the clock and the data transmission interval. TM is the monostable trigger time. N is the transmission bits. The transmission bits can be arbitrary, but in actual use, 13 bits are used for single cycle encoder and 25 bits are used for multiple cycles. For the slave encoder, it is impossible to know the number of clock pulses sent by the master in advance, Therefore, it is impossible to determine the start bit and stop bit of the frame. The solution to the problem is to use the high potential to remain unchanged for a period of time as the frame end flag. TM monostable time refers to this time. In practical application, a monostable (software or hardware) can be used, and the clock input can be used as the monostable input, Control the data output state of SSI through monostable output: once monostable is set, the output state of SSI will return to the initial state, ready to start the next data cycle process.

BISS communication protocol

BISS communication protocol is a full duplex synchronous serial bus communication protocol, which is specially designed to meet the real-time, bidirectional and high-speed sensor communication. It is compatible with the industrial standard SSI (synchronous serial interface protocol) bus protocol in hardware. Its typical application is to realize the communication between servo driver and encoder in the field of motion control. BISS, developed by German ic-haus company, has become an international standard of sensor communication protocol. The current version of BISS communication protocol is biss-c.

Key technical features:

1. Two wire serial synchronous data bus, RS422 interface, baud rate up to 10mbit / S; LVDS interface is adopted, and the baud rate is > 10mbit / s, which reflects the high response speed of BISS;

2. High communication efficiency, more than 64 bits are transmitted per 10us, and the payload rate is greater than 80%. This reflects that BISS can carry high-resolution encoder data;

3. Line time division multiplexing includes a data communication channel transmitting one frame in each communication cycle and a register communication channel transmitting one frame bit. Among them, register communication and data communication are completely independent and do not interfere with each other. For applications that do not require register communication, biss-c unidirectional version can be used. This version of the protocol has no register communication. This reflects that the control system using BISS has better stability and convenience.

4. Various security mechanisms ensure reliable data. BISS‘s delay compensation technology can compensate the signal delay caused by the transmission line. Two sets of CRC generated polynomials are used to verify the sensor data and register data respectively. The BISS protocol frame also includes an alarm bit and an error bit. The CRC generation polynomial can be customized. This reflects that BISS transmission is reliable and the control system using BISS is reliable.

5. Data synchronization: BISS uses the clock signal to synchronize the sensor data. The sensor updates the data when the first clock pulse arrives. The transmission delay of each frame of data arriving at the subsequent electronic equipment is the same, which is convenient for the subsequent electronic equipment to compensate the delay. It is especially suitable for applications requiring strict time position relationship, such as motor control. This reflects that BISS has little impact on the encoder accuracy and helps to improve the high-speed characteristics of the control system.

6. Networking capability. A single bus sensor ring network can be formed through BISS. All sensor data can be collected in one communication cycle, and the signal acquisition is synchronous. This reflects the expansibility and foresight of BISS.

7. Plug and play, BISS supports reading encoder parameters from registers to configure data communication. All encoders and control systems that support BISS standard EDS and profile can communicate directly without modifying any program.

Networking mode:

The figure shows the basic networking mode of BISS, which is called point-to-point mode. The subsequent electronic equipment (PLC in the figure) provides the clock to the sensor through the differential signal, and the sensor synchronously sends the sensing data to the subsequent electronic equipment through the differential signal. In the BISS protocol, the subsequent electronic device is called master and the sensor is called slave. In the point-to-point mode, the master can receive the slave data and conduct two-way data communication with the slave at the same time.

Frame structure and data communication:

The BISS communication frame in point to point networking is described. Ma is sent by the master to drive communication, and SL is the data signal sent by slave. Completing one BISS communication frame means that the master receives one frame of data.

EnDat protocol

EnDat interface is a digital, full duplex synchronous serial data transmission protocol designed by Heidenhain for encoders. It can not only transmit position values for incremental and absolute encoders, but also transmit or update the information stored in the encoder or save new information. Because the serial transmission mode is used, only four signal lines are needed. Under the clock excitation of the subsequent power equipment, the data information is transmitted synchronously. The data type (position value, parameter, diagnostic information, etc.) is determined by the mode command sent by the subsequent electronic equipment to the encoder.

characteristic:

1. The transmission position value and additional information can be transmitted at the same time; The type of additional information can be selected by storing the address selection code.

2. The encoder data storage area includes encoder manufacturer parameters, OEM manufacturer parameters, operation parameters and operation status, which is convenient for the system to realize parameter configuration.

3. Endat2.2 encoder realizes all digital transmission, and the incremental signal processing is completed inside the encoder (built-in 14bit subdivision), which improves the quality and reliability of signal transmission and can achieve higher resolution.

4. Monitoring and diagnosis function. Alarm conditions include: failure of light source, insufficient signal amplitude, wrong position calculation, too low or too high operating voltage, too large current consumption, etc; A warning signal is provided when some limit values of the encoder are approached or exceeded.

5. Wider voltage range (3.6-14v) and transmission rate (16m)

Data acquisition schematic diagram of EnDat interface encoder

Data transmission format

During synchronous data transmission of each frame, a data packet is sent, and the transmission cycle starts from the first falling edge of the clock. The measured value is saved and the position value is calculated. After two clock pulses (2t), the subsequent electronic equipment sends the mode command "encoder transmission position value" (with or without additional information).

After calculating the absolute position value, the encoder transmits data to subsequent electronic devices from the start bit, and the subsequent error bits F1 and F2 (only exist in endat2.2 instruction) It is a group signal serving all monitoring functions and fault monitoring. Their generation is independent of each other. It is used to represent the encoder fault that may lead to incorrect location information. The exact cause of the fault is saved in the "running state" storage area and can be queried by subsequent powered equipment.

From the lowest bit, the absolute position value is transmitted, and the length of the data is determined by the type of encoder used. The number of clock pulses required to transmit the position value is saved in the parameters of the encoder manufacturer. The transmission of position value data ends with cyclic redundancy detection code.

Hiperface protocol

Hiperface is the abbreviation of high performance interface. It is the standard interface of sick-stepmann motor feedback system. The interface is specially developed for digital drive control and provides users with standardized simplified mechanical and electrical interfaces.