Application Note

Application Note: AS5048 SPI Sensor Readout
AS5048A
14-bit Rotary Position Sensor with Digital Interface
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Revision 1.1 / 2013/06/26
AS5048 SPI Sensor Readout
Table of Contents
1.
General Description ............................................................................................................... 2
2.
Reading the AS5048A using SPI ........................................................................................... 2
3.
Sensor Output Averageing .................................................................................................... 4
4.
Parity calculation ................................................................................................................... 4
5.
AS5048A SPI Register Map .................................................................................................. 5
6.
Ordering Information .............................................................................................................. 6
Copyright ....................................................................................................................................... 7
Disclaimer ..................................................................................................................................... 7
Revision History
Revision
Date
Owner
Description
1.0
03.28.2013
rph
Initial Version
1.1
26.06.2013
rph
Updated Averaging Description
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AS5048 SPI Sensor Readout
1.
General Description
This Application Note explains how to communicate with the AS5048 14-bit Rotary Position
Sensor. There are two versions of the AS5048 available:
Table 1:
AS5048 versions
Ordering Code
AS5048A
AS5048B
Digital Angle Interface
SPI
I2C
Find more information on our webpage:
http://ams.com/eng/Products/Magnetic-Position-Sensors
2.
Reading the AS5048A using SPI
The AS5048A comes with SPI interface. Following example shows how to read the AS5048A.
Example:
#define SPI_CMD_READ 0x4000 // flag indicating read attempt
#define SPI_CMD_WRITE 0x8000 // flag indicating write attempt
#define SPI_REG_AGC 0x3ffd // agc register when using SPI
#define SPI_REG_MAG 0x3ffe // magnitude register when using SPI
#define SPI_REG_DATA 0x3fff // data register when using SPI
#define SPI_REG_CLRERR 0x1 // clear error register when using SPI
#define SPI_REG_ZEROPOS_HI 0x0016 // zero position register high byte
#define SPI_REG_ ZEROPOS_LO 0x0017 // zero position register low byte
void spiReadData()
{
u16 dat; // 16-bit data buffer for SPI communication
u16 magreg;
ushort angle, agcreg;
ubyte agc;
ushort value;
bit alarmHi, alarmLo;
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AS5048 SPI Sensor Readout
/* Send READ AGC command. Received data is thrown away: this data comes
from the previous command (unknown)*/
dat = SPI_CMD_READ | SPI_REG_AGC;
dat |= spiCalcEvenParity(dat) << 15;
spiTransfer((u8*)&dat, sizeof(u16));
/* Send READ MAG command. Received data is the AGC value: this data comes
from the previous command (unknown)*/
dat = SPI_CMD_READ | SPI_REG_MAG;
dat |= spiCalcEvenParity(dat) << 15;
spiTransfer((u8*)&dat, sizeof(u16));
magreg = dat;
/* Send READ ANGLE command. Received data is the MAG value, from the
previous command */
dat = SPI_CMD_READ | SPI_REG_DATA;
dat |= spiCalcEvenParity(dat) << 15;
spiTransfer((u8*)&dat, sizeof(u16));
agcreg = dat;
/* Send NOP command. Received data is the ANGLE value, from the previous
command */
dat = 0x0000; // NOP command.
spiTransfer((u8*)&dat, sizeof(u16));
angle = dat >> 2;
}
if ((dat & 0x4000) || (agcreg & 0x4000) || (magreg & 0x4000))
{
/* error flag set - need to reset it */
dat = SPI_CMD_READ | SPI_REG_CLRERR;
dat |= spiCalcEvenParity(dat)<<15;
spiTransfer((u8*)&dat, sizeof(u16));
}
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AS5048 SPI Sensor Readout
else
{
agc = agcreg & 0xff // AGC value (0..255)
value = dat & (16384 - 31 - 1); // Angle value (0.. 16384 steps)
angle = (value * 360) / 16384; // Angle value in degree (0..359.9°)
magnitude = magreg & (16384 - 31 - 1);
alarmLo = (agcreg >> 10) & 0x1;
alarmHi = (agcreg >> 11) & 0x1;
}
3.
Sensor Output Averageing
The code example below shows an easy averaging algorithm to reduce noise of the angular
output for angular values within one rotation and with no zero crossing of the output data.
Note: As 360° is the same as 0° this would cause an averaging error. To perform averaging of
output data with more than one rotation refer to “Mean of circular quantities”.
Example:
#define average 100
for (count = average; count; count--)
{
data = sensor_read(); //reading,computing sensor output
position += data;
}
position = position / average;
4.
Parity calculation
Following example shows how the parity of a 16bit unsigned integer can be calculated.
Example:
static u8 spiCalcEvenParity(ushort value)
{
u8 cnt = 0;
u8 i;
for (i = 0; i < 16; i++)
{
if (value & 0x1) cnt++;
value >>= 1;
}
return cnt & 0x1;
}
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AS5048 SPI Sensor Readout
5.
AS5048A SPI Register Map
The available registers for SPI communication of the AS5048A are listed in Figure 1.
Figure 1:
SPI Register Map
Address
hex
Readout Registers
Programmable Customer settings
Control and Error Registers
x0000
Name
SPI NOP
x0001 Clear Error Flag
x0003
Programming
Control
OTP Register
x0016
Zero Position Hi
x0017
OTP Register
Zero Position
Low 6 LSBs
Diagnostics +
x3FFD Automatic Gain
Control (AGC)
Access
Type Bit Nr.
R
R
R/W
R/W
+
Program
R/W
+
Program
R
x3FFE
Magnitude
R
x3FFF
Angle
R
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13
:
0
13
:
3
2
1
0
13
:
7
6
5
4
3
2
1
0
13
:
8
7
:
0
13
:
6
5
:
0
13
12
11
10
9
8
7
:
0
13
:
0
13
:
0
Symbol
Default
NOP
0
not used
n.a.
Parity Error
Command Invalid
Framing Error
Description
No operation dummy information
Error Register. All errors are cleared by access
0
not used
Verify
not used
0
Burn
Programming control register.
Programming must be enabled before burning the
fuse(s). After programming is a verification mandatory.
See programming procedure.
reserved
Programming Enable
not used
0
Zero Position <13>
:
Zero Position <6>
0
:
0
not used
0
Zero Position <5>
:
Zero Position <0>
0
:
0
not used
n.a.
Comp High
Comp Low
COF
OCF
AGC value<7>
:
AGC value<0>
Magnitude<13>
:
Magnitude<0>
Angle <13>
:
Angle<0>
0
0
0
1
1
:
0
0
:
0
0
:
0
Zero Position value high byte
Revision 1.1 / 26/06/13
Zero Position remaining 6 lower LSB's
Diagnostics flags
Automatic Gain Control value.
0 decimal represents high magnetic field
255 decimal represents low magnetic field
Magnitude information after ATAN calculation
Angle information after ATAN calculation
and zero position adder
page 5/8
AS5048 SPI Sensor Readout
6.
Ordering Information
Table 2:
Ordering Information
Ordering Code
Description
comments
AS5048A-EK-AB-STM1.0
AS5048A Eval-Kit for stepper motor
SPI interface
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AS5048 SPI Sensor Readout
Copyright
Copyright © 1997-2013, ams AG, Tobelbader Strasse 30, 8141 Unterpremstaetten, Austria-Europe.
Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged,
translated, stored, or used without the prior written consent of the copyright owner.
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Disclaimer
Devices sold by ams AG are covered by the warranty and patent indemnification provisions appearing in its
Term of Sale. ams AG makes no warranty, express, statutory, implied, or by description regarding the
information set forth herein or regarding the freedom of the described devices from patent infringement. ams
AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior to
designing this product into a system, it is necessary to check with ams AG for current information.
This product is intended for use in normal commercial applications. Applications requiring extended
temperature range, unusual environmental requirements, or high reliability applications, such as military,
medical life-support or lifesustaining equipment are specifically not recommended without additional
processing by ams AG for each application. For shipments of less than 100 parts the manufacturing flow might
show deviations from the standard production flow, such as test flow or test location.
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damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or consequential
damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical
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technical or other services.
Contact Information
Headquarters
ams AG
Tobelbader Strasse 30
8141 Unterpremstaetten
Austria
T. +43 (0) 3136 500 0
For Sales Offices, Distributors and Representatives, please visit:
http://www.ams.com/contact
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