Description
The TMC8100 includes a programmable microcontroller optimized for serial synchronous and asynchronous absolute encoder protocols up to 16Mbit/s. It can replace dedicated encoder protocol interface ICs and field programmable gate array/FPGA implementations while supporting in-system updates for different encoder capabilities or for switching to other encoder protocols. The TMC8100 is a compact, cost-effective, and flexible communication solution for adding absolute encoder support to industrial drives.
This application note provides details on the TMC8100 software reference implementation supporting absolute position encoder with synchronous serial interface (SSI).
Features
- SSI Implementation
- Example Uses 1MHz Clock Frequency
- Gray to Binary Code Conversion
- Input Filter
- SSI Clock Frequencies up to 16MHz Possible
Applications
- Motor Position Feedback
System Description
Servo motor drives, e.g., in industrial applications typically require accurate, reliable, and low-latency position feedback. For a long time, optical encoders with incremental A/B/N output have been the industry standard. Nevertheless, absolute position encoders are gaining traction often with additional functionality and different interface protocols (mostly vendor-specific). An example is the SSI protocol for synchronous serial transfer of digital data between encoder and controller. It uses two separate connections – one for the clock generated by the controller and one for the encoder data shifted out from the encoder. The physical layer is based on the RS422 standard and capable of transmitting position values and diagnostic information from encoder to controller.
The encoder used in this example with an SSI connects to the TMC8100-EVAL-KIT through a single cable with six wires being used (Figure 1). The six wires are as follows:
- +24V and GND: encoder power supply and ground connection
- DATA+ and DATA-: differential RS-422 signals for transmission of data from encoder to controller
- CLK+ and CLK-: differential RS-422 signals for transmission of clock from controller to encoder
The reference implementation features:
- Generating of clock signal with the required frequency, number of pulses, and polarity
- 1Mbps data rate as supported by the SSI encoder
- Packing and unpacking of data
- Conversion of 16-bit encoder position data from gray code to 16-bit binary code
The reference implementation is available as source code. Users may use this as a starting point and apply changes as required by the application.
System Overview
The provided software has been designed to operate in conjunction with the TMC8100-EVAL-KIT and tested with the Ri360P0-QR14-ESG25X2 encoder (Turck) with SSI.
