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flexio_endat2_polling_transfer

flexio_endat2_polling_transfer#

Overview#

The flexio_endat2_polling_transfer example shows how to use FlexIO as an EnDat2 master in polling mode.

In this example, the FRDM-MCXA366 board connects to an EnDat encoder through an RS-485 interface. FlexIO sends the position command, generates the encoder clock, controls the data direction, receives the position frame, and checks the EnDat CRC5. The decoded multi-turn position, single-turn position, encoder error bit, and CRC result are printed through the debug console.

The default encoder profile is EQI1331_810662-03 with a 12-bit multi-turn field, a 19-bit single-turn field, one error bit, and a 15 MHz EnDat clock.

Supported Boards#

FRDM-MCXA366
Hardware requirements

  • USB Type-C cable

  • FRDM-MCXA366 board

  • EQI1331_810662-03 absolute encoder

  • EnDat2 RS-485 electrical interface and encoder power supply

  • Personal Computer

Board settings

This example requires connecting the FRDM-MCXA366 board to an EnDat2 encoder through an RS-485 electrical interface that meets the encoder voltage and line-driver requirements.

  • MCXA366 P2_8 (FLEXIO0_D16) -> TXD input of the RS-485 interface

  • MCXA366 P2_9 (FLEXIO0_D17) <- RXD output of the RS-485 interface

  • MCXA366 P2_10 (FLEXIO0_D18) -> CLK input of the RS-485 interface

  • MCXA366 P2_11 (FLEXIO0_D19) -> DIR input of the RS-485 interface

  • FRDM-MCXA366 GND -> encoder interface GND

  • Remove the external pull-up on RXD and enable the internal pull-down on P2_9 (FLEXIO0_D17)

The internal pull-down on RXD is required because the RS-485 receiver’s RO output is high-impedance while idle, so RXD must read low for the example to correctly detect the first RXD rising edge after DIR goes low as the EnDat2 Start bit.

The validated encoder profile uses the following settings:

  • FlexIO root clock: 60 MHz (PLL1_DIV)

  • EnDat2 bit rate: 15 MHz

  • Multi-turn position: 12 bits

  • Single-turn position: 19 bits

  • ERR1: 1 bit

  • CRC5 polynomial x^5 + x^3 + x^1 + 1

Prepare the Demo

  1. Connect the EQI1331_810662-03 encoder and its RS-485 electrical interface to the FRDM-MCXA366 board.

  2. Power the encoder and confirm the interface logic voltage is compatible with the MCXA366 I/O voltage.

  3. Connect a USB Type-C cable between the host PC and the board’s MCU-Link USB port.

  4. Open a serial terminal with the following settings:

    • 115200 baud rate

    • 8 data bits

    • No parity

    • One stop bit

    • No flow control

  5. Download the program to the target board.

  6. Either press the reset button on your board or launch the debugger in your IDE to begin running the example.

Running the demo

When the example runs successfully, information similar to the following is printed in the terminal window.

MCXA366 FlexIO EnDat2 demo
Encoder: EQI1331_810662-03, MT=12, ST=19, bitrate=15000000 bps
FlexIO clock: 60000000 Hz
Pins: TXD=FLEXIO0_D16, RXD=FLEXIO0_D17, CLK=FLEXIO0_D18, DIR=FLEXIO0_D19

MT=2750, ST=519896, ERR1=0, CRC=OK
MT=2751, ST=201629, ERR1=0, CRC=OK

ERR1 is the raw error bit received from the encoder. CRC=OK means the received frame passed CRC5 validation.

If No EnDat2 start bit detected is printed, check the RXD idle level, the DIR polarity, the RS-485 receiver enable wiring, the encoder power, and the differential DATA wiring. If CRC=FAIL is printed repeatedly, check the configured bit rate and field lengths, signal integrity, clock/data polarity, and termination.

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