Saxion Lectoraat MT / AS5048

AS5048A SPI - Magnetic rotary encoder library

Library for communication over the SPI interface with the ams.com AS5048A magnetic rotary encoder.

Example:

Simple readout of a single angle measurement from a single sensor on the SPI-bus

#include "mbed.h"
#include <as5048spi.h>

// The sensors connection are attached to pins 5-8
As5048Spi sensor(p5, p6, p7, p8);
Serial pc(USBTX, USBRX); // tx, rx

int main() {
    while(1) {
        // 
        const int* angles = sensor.read_angle();
        int angle = angles[0];
        
        // The read angle returns the value returned over the SPI bus, including parity bit
        pc.printf("Read result: %x\r\n", angle);
        
        if( As5048Spi::parity_check(angle) )
        {
            // Convert range from 0 to 2^14-1 to 0 - 360 degrees
            int degrees = As5048Spi::degrees(angle)/100;
            pc.printf("Parity check succesfull.\r\n");
            pc.printf("Angle: %i degrees\r\n", degrees );
        }
        else
        {
            pc.printf("Parity check failed.\r\n");
        }
            
        wait_ms(500);
    }
}

The class supports daisy chaining multiple sensors on the SPI-bus as well. See: SPI-Daisy-Chaining.

as5048spi.h

Committer:
JSpikker
Date:
2015-03-17
Revision:
4:06b89a41109e
Parent:
3:a8ad32e439d4

File content as of revision 4:06b89a41109e:

#include "mbed.h"
typedef enum {
    AS_FLAG_PARITY = 0x8000,
    AS_FLAG_READ = 0x4000,
} As5048Flag;

typedef enum {
    AS_CMD_NOP = 0x0000,
    AS_CMD_ERROR = 0x0001 | AS_FLAG_READ,       // Reads error register of sensor and clear error flags
    AS_CMD_DIAGNOSTICS = 0x3FFD |  AS_FLAG_READ, // Reads automatic gain control and diagnostics info
    AS_CMD_MAGNITUDE = 0x3FFE | AS_FLAG_READ,
    
    AS_CMD_ANGLE = 0x3FFF| AS_FLAG_PARITY | AS_FLAG_READ,
} As5048Command;

// Masks for bits in the result of the AS_CMD_DIAGNOSTICS command
typedef enum {
    AS_DIAG_CORDIC_OVERFLOW = 0x0200,
    AS_DIAG_HIGH_MAGNETIC = 0x0400,
    AS_DIAG_LOW_MAGNETIC = 0x0800,
} As5048Diagnostics;


//! Class for interfacing with the AMS AS5048A magnetic rotary sensor over the SPI-interface.
class As5048Spi
{
public:
    As5048Spi(PinName mosi, PinName miso, PinName sclk, PinName chipselect, int nDevices = 1);
    ~As5048Spi();
    
    bool error(int device = -1);
    
    /// Sets the SPI clock frequency in Hz. Maximum tested frequency is 10MHz.
    void frequency(int frequency = 1000000);
    
    /// Sends a read command to the sensor.
    const int* read(As5048Command command);
    
    /// Sends a read command to the sensor. 
    /// A call to this function will not directly return the requested value. The
    /// requested value will be returned in a next read_sequential call. 
    /// Use this function to read sensor values with minimum speed impact on SPI-bus
    /// and microcontroller.
    const int* read_sequential(As5048Command command);
    
    /// Performs a single angle measurement on all sensors
    /// @return Array of raw angle data. To get the 14-bit value representing
    ///     the angle, apply the mask() to the result.
    const int* read_angle();
    
    /// Performs sequential angle measurements on all sensors. The first time this
    /// method is called the result is not usefull, the measurement data of the call
    /// will be returned by the next call to this method.
    /// @return Array of raw angle data. To get the 14-bit value representing
    ///     the angle, apply the mask() to the result.
    const int* read_angle_sequential();

    /// Returns lowest 14-bits
    static int mask(int sensor_result);

    /// Applies the mask to the first n bytes in the read buffer (for daisychained sensors).
    static void mask(int* sensor_results, int n);
    
    /// Checks if the return value from the sensor has the right parity
    /// @return true if ok
    static bool parity_check(int sensor_result);
    
    /// Returns an angle from 0 to 36000 (degrees times 100).
    /// @param sensor_result is one of the values returned by read_angle or read_angle_sequential
    static int degrees(int sensor_result);
    
    /// Returns an angle from 0 to 2*PI*100 
    /// @param sensor_result is one of the values returned by read_angle or read_angle_sequential
    static int radian(int sensor_result);
    

protected:
    int _nDevices;
    DigitalOut _chipSelectN;
    SPI _spi;
    
    int* _readBuffer; // Stores the results of the last sequential read
    
    int* _read(As5048Command command);
};