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.

Diff: as5048spi.cpp

Revision:
0:3edcf58e51e7
Child:
1:f2ed22514649
diff -r 000000000000 -r 3edcf58e51e7 as5048spi.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/as5048spi.cpp	Thu Sep 18 10:20:22 2014 +0000
@@ -0,0 +1,131 @@
+#include "as5048spi.h"
+
+
+
+
+
+As5048Spi::As5048Spi(PinName mosi, PinName miso, PinName sclk, PinName chipselect, int ndevices) :
+    _nDevices(ndevices),
+    _chipSelectN(chipselect),
+    _spi(mosi, miso, sclk)
+{
+    _chipSelectN.write(1);
+    // AS5048 needs 16-bits for is commands
+    // Mode = 1: 
+    //  clock polarity = 0 --> clock pulse is high
+    //  clock phase = 1 --> sample on falling edge of clock pulse
+    _spi.format(16, 1);
+    
+    // Set clock frequency to 1 MHz (max is 10Mhz)
+    _spi.frequency(10000000);
+    
+    _readBuffer = new int[ndevices];
+}
+
+As5048Spi::~As5048Spi()
+{
+    delete [] _readBuffer;
+}
+
+int As5048Spi::degrees(int sensor_result)
+{
+    return mask(sensor_result) * 36000 / 0x4000;
+}
+
+
+int As5048Spi::radian(int sensor_result)
+{
+    return mask(sensor_result) * 62832 / 0x4000;
+}
+
+bool As5048Spi::error(int device)
+{
+    if( device == -1 ) {
+        for(int i = 0; i < _nDevices; ++i) {
+            if( _readBuffer[i] & 0x4000 ) {
+                return true;
+            }
+        }
+    } else if( device < _nDevices ) {
+        return (_readBuffer[device] & 0x4000) == 0x4000;
+    }
+    return false; 
+}
+
+
+void As5048Spi::frequency(int hz) 
+{
+    _spi.frequency(hz);
+}
+
+int As5048Spi::mask(int sensor_result)
+{
+    return sensor_result & 0x3FFF; // return lowest 14-bits
+}
+
+bool As5048Spi::parity_check(int sensor_result)
+{
+    // Use the LSb of result to keep track of parity (0 = even, 1 = odd)
+    int result = sensor_result;
+    
+    for(int i = 1; i <= 15; ++i) {
+        sensor_result >>= 1;
+        result ^= sensor_result;
+    }
+    // Parity should be even
+    return (result & 0x0001) == 0;
+}
+
+const int* As5048Spi::read(As5048Command command)
+{
+    _read(command); // Send command to device(s)
+    return _read(AS_CMD_NOP); // Read-out device(s)
+}
+
+const int*  As5048Spi::read_sequential(As5048Command command)
+{
+    return _read(command);
+}
+
+const int*  As5048Spi::read_angle()
+{  
+    _read(AS_CMD_ANGLE); // Send command to device(s)
+    return _read(AS_CMD_NOP); // Read-out device(s)
+}
+
+const int*  As5048Spi::read_angle_sequential()
+{
+    return _read(AS_CMD_ANGLE); 
+}
+
+
+int* As5048Spi::_read(As5048Command command)
+{
+    if(_nDevices == 1)
+    {
+        // Give command to start reading the angle
+        _chipSelectN.write(0);
+        wait_us(1); // Wait at least 350ns after chip select
+        _readBuffer[0] = _spi.write(command);
+        _chipSelectN.write(1);
+        wait_us(1); // Wait at least 350ns after chip select
+    } else
+    {
+        // Enable the sensor on the chain
+        _chipSelectN.write(0);
+         wait_us(1); // Wait at least 350ns after chip select
+        for(int i = 0; i < _nDevices; ++i)
+        {
+            _readBuffer[i] = _spi.write(command);
+        }
+        _chipSelectN.write(1);
+        wait_us(1); // Wait at least 350ns after chip select
+    }
+    return _readBuffer;
+}
+
+
+
+
+
+    
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