Texas TMS320x2833x User manual

TMS320x2833x, 2823x Enhanced QuadratureEncoder Pulse (eQEP) Module
Reference Guide
Literature Number: SPRUG05AAugust 2008 – Revised December 2008

2 SPRUG05A – August 2008 – Revised December 2008Submit Documentation Feedback

Contents
Preface ........................................................................................................................................ 61 Introduction ......................................................................................................................... 82 Description ........................................................................................................................ 102.1 EQEP Inputs ............................................................................................................. 112.2 Functional Description .................................................................................................. 112.3 eQEP Memory Map ..................................................................................................... 123 Quadrature Decoder Unit (QDU) ........................................................................................... 143.1 Position Counter Input Modes ......................................................................................... 143.2 eQEP Input Polarity Selection ......................................................................................... 173.3 Position-Compare Sync Output ........................................................................................ 174 Position Counter and Control Unit (PCCU) ............................................................................ 174.1 Position Counter Operating Modes.................................................................................... 174.2 Position Counter Latch .................................................................................................. 204.3 Position Counter Initialization .......................................................................................... 224.4 eQEP Position-compare Unit .......................................................................................... 225 eQEP Edge Capture Unit ..................................................................................................... 246 eQEP Watchdog ................................................................................................................. 277 Unit Timer Base ................................................................................................................. 278 eQEP Interrupt Structure ..................................................................................................... 289 eQEP Registers .................................................................................................................. 28
SPRUG05A – August 2008 – Revised December 2008 Table of Contents 3Submit Documentation Feedback

www.ti.com
List of Figures
1 Optical Encoder Disk ........................................................................................................ 82 QEP Encoder Output Signal for Forward/Reverse Movement ......................................................... 93 Index Pulse Example ........................................................................................................ 94 Functional Block Diagram of the eQEP Peripheral .................................................................... 125 Functional Block Diagram of Decoder Unit ............................................................................. 146 Quadrature Decoder State Machine ..................................................................................... 157 Quadrature-clock and Direction Decoding .............................................................................. 168 Position Counter Reset by Index Pulse for 1000 Line Encoder (QPOSMAX = 3999 or 0xF9F) ................. 189 Position Counter Underflow/Overflow (QPOSMAX = 4) .............................................................. 1910 Software Index Marker for 1000-line Encoder (QEPCTL[IEL] = 1) .................................................. 2111 Strobe Event Latch (QEPCTL[SEL] = 1) ................................................................................ 2112 eQEP Position-compare Unit ............................................................................................. 2213 eQEP Position-compare Event Generation Points ..................................................................... 2314 eQEP Position-compare Sync Output Pulse Stretcher ................................................................ 2315 eQEP Edge Capture Unit ................................................................................................. 2516 Unit Position Event for Low Speed Measurement (QCAPCTL[UPPS] = 0010) .................................... 2517 eQEP Edge Capture Unit - Timing Details .............................................................................. 2618 eQEP Watchdog Timer .................................................................................................... 2719 eQEP Unit Time Base ..................................................................................................... 2820 EQEP Interrupt Generation ............................................................................................... 2821 QEP Decoder Control (QDECCTL) Register ........................................................................... 2922 eQEP Control (QEPCTL) Register ....................................................................................... 3023 eQEP Position-compare Control (QPOSCTL) Register ............................................................... 3124 eQEP Capture Control (QCAPCTL) Register .......................................................................... 3225 eQEP Position Counter (QPOSCNT) Register ......................................................................... 3326 eQEP Position Counter Initialization (QPOSINIT) Register........................................................... 3327 eQEP Maximum Position Count Register (QPOSMAX) Register .................................................... 3328 eQEP Position-compare (QPOSCMP) Register........................................................................ 3329 eQEP Index Position Latch (QPOSILAT) Register .................................................................... 3430 eQEP Strobe Position Latch (QPOSSLAT) Register .................................................................. 3431 eQEP Position Counter Latch (QPOSLAT) Register .................................................................. 3432 eQEP Unit Timer (QUTMR) Register .................................................................................... 3533 eQEP Register Unit Period (QUPRD) Register ........................................................................ 3534 eQEP Watchdog Timer (QWDTMR) Register .......................................................................... 3535 eQEP Watchdog Period (QWDPRD) Register ......................................................................... 3536 eQEP Interrupt Enable (QEINT) Register ............................................................................... 3637 eQEP Interrupt Flag (QFLG) Register ................................................................................... 3738 eQEP Interrupt Clear (QCLR) Register.................................................................................. 3839 eQEP Interrupt Force (QFRC) Register ................................................................................. 3940 eQEP Status (QEPSTS) Register ........................................................................................ 4041 eQEP Capture Timer (QCTMR) Register ............................................................................... 4142 eQEP Capture Period (QCPRD) Register .............................................................................. 4143 eQEP Capture Timer Latch (QCTMRLAT) Register ................................................................... 4144 eQEP Capture Period Latch (QCPRDLAT) Register .................................................................. 42
List of Figures4 SPRUG05A – August 2008 – Revised December 2008Submit Documentation Feedback

www.ti.com
List of Tables
1 EQEP Memory Map ....................................................................................................... 122 Quadrature Decoder Truth Table ........................................................................................ 153 eQEP Decoder Control (QDECCTL) Register Field Descriptions ................................................... 294 eQEP Control (QEPCTL) Register Field Descriptions................................................................. 305 eQEP Position-compare Control (QPOSCTL) Register Field Descriptions ......................................... 316 eQEP Capture Control (QCAPCTL) Register Field Descriptions .................................................... 327 eQEP Position Counter (QPOSCNT) Register Field Descriptions ................................................... 338 eQEP Position Counter Initialization (QPOSINIT) Register Field Descriptions .................................... 339 eQEP Maximum Position Count (QPOSMAX) Register Field Descriptions ........................................ 3310 eQEP Position-compare (QPOSCMP) Register Field Descriptions ................................................. 3411 eQEP Index Position Latch(QPOSILAT) Register Field Descriptions ............................................... 3412 eQEP Strobe Position Latch (QPOSSLAT) Register Field Descriptions ............................................ 3413 eQEP Position Counter Latch (QPOSLAT) Register Field Descriptions ............................................ 3414 eQEP Unit Timer (QUTMR) Register Field Descriptions .............................................................. 3515 eQEP Unit Period (QUPRD) Register Field Descriptions ............................................................. 3516 eQEP Watchdog Timer (QWDTMR) Register Field Descriptions .................................................... 3517 eQEP Watchdog Period (QWDPRD) Register Field Description .................................................... 3618 eQEP Interrupt Enable(QEINT) Register Field Descriptions ......................................................... 3619 eQEP Interrupt Flag (QFLG) Register Field Descriptions ............................................................. 3720 eQEP Interrupt Clear (QCLR) Register Field Descriptions ........................................................... 3821 eQEP Interrupt Force (QFRC) Register Field Descriptions ........................................................... 3922 eQEP Status (QEPSTS) Register Field Descriptions ................................................................. 4023 eQEP Capture Timer (QCTMR) Register Field Descriptions ......................................................... 4124 eQEP Capture Period Register (QCPRD) Register Field Descriptions ............................................. 4125 eQEP Capture Timer Latch (QCTMRLAT) Register Field Descriptions ............................................ 4226 eQEP Capture Period Latch (QCPRDLAT) Register Field Descriptions ............................................ 42
SPRUG05A – August 2008 – Revised December 2008 List of Tables 5Submit Documentation Feedback

PrefaceSPRUG05A – August 2008 – Revised December 2008
Read This First
This reference guide describes the enhanced quadrature encoder pulse (eQEP) module.
About This Manual
The eQEP module described in this reference guide is a Type 0 eQEP. See the TMS320x28xx, 28xxxDSP Peripheral Reference Guide (SPRU566 ) for a list of all devices with a module of the same type todetermine the differences between types and for a list of device-specific differences within a type.
Notational Conventions
This document uses the following conventions.•Hexadecimal numbers are shown with the suffix h or with a leading 0x. For example, the followingnumber is 40 hexadecimal (decimal 64): 40h or 0x40.•Registers in this document are shown in figures and described in tables.– Each register figure shows a rectangle divided into fields that represent the fields of the register.Each field is labeled with its bit name, its beginning and ending bit numbers above, and itsread/write properties below. A legend explains the notation used for the properties.– Reserved bits in a register figure designate a bit that is used for future device expansion.
Related Documentation From Texas InstrumentsThe following books describe the TMS320x2833x/2823x devices and related support tools that areavailable on the TI website:
Data Manual and Errata—SPRS439— TMS320F28335, TMS320F28334, TMS320F28332, TMS320F28235, TMS320F28234,TMS320F28232 Digital Signal Controllers (DSCs) Data Manual contains the pinout, signaldescriptions, as well as electrical and timing specifications for the F2833x/2823x devices.
SPRZ272— TMS320F28335, F28334, F28332, TMS320F28235, F28234, F28232 Digital SignalControllers (DSCs) Silicon Errata describes the advisories and usage notes for different versions ofsilicon.
CPU User's Guides—SPRU430— TMS320C28x DSP CPU and Instruction Set Reference Guide describes the centralprocessing unit (CPU) and the assembly language instructions of the TMS320C28x fixed-pointdigital signal processors (DSPs). It also describes emulation features available on these DSPs.
SPRUEO2— TMS320C28x Floating Point Unit and Instruction Set Reference Guide describes thefloating-point unit and includes the instructions for the FPU.
Peripheral Guides—
SPRU566— TMS320x28xx, 28xxx DSP Peripheral Reference Guide describes the peripheral referenceguides of the 28x digital signal processors (DSPs).
SPRUFB0— TMS320x2833x, 2823x System Control and Interrupts Reference Guide describes thevarious interrupts and system control features of the 2833x digital signal controllers (DSCs).
SPRU812— TMS320x2833x, 2823x Analog-to-Digital Converter (ADC) Reference Guide describes how toconfigure and use the on-chip ADC module, which is a 12-bit pipelined ADC.
6Preface SPRUG05A – August 2008 – Revised December 2008Submit Documentation Feedback

www.ti.com Related Documentation From Texas Instruments
SPRU949— TMS320x2833x, 2823x External Interface (XINTF) User's Guide describes the XINTF, whichis a nonmultiplexed asynchronous bus, as it is used on the 2833x devices.
SPRU963— TMS320x2833x, TMS320x2823x Boot ROM User's Guide describes the purpose andfeatures of the bootloader (factory-programmed boot-loading software) and provides examples ofcode. It also describes other contents of the device on-chip boot ROM and identifies where all ofthe information is located within that memory.
SPRUFB7— TMS320x2833x, 2823x Multichannel Buffered Serial Port (McBSP) User's Guide describesthe McBSP available on the F2833x devices. The McBSPs allow direct interface between a DSPand other devices in a system.
SPRUFB8— TMS320x2833x, 2823x Direct Memory Access (DMA) Reference Guide describes the DMAon the 2833x devices.
SPRUG04— TMS320x2833x, 2823x Enhanced Pulse Width Modulator (ePWM) Module Reference Guidedescribes the main areas of the enhanced pulse width modulator that include digital motor control,switch mode power supply control, UPS (uninterruptible power supplies), and other forms of powerconversion.
SPRUG02— TMS320x2833x, 2823x High-Resolution Pulse Width Modulator (HRPWM) describes theoperation of the high-resolution extension to the pulse width modulator (HRPWM).
SPRUFG4— TMS320x2833x, 2823x Enhanced Capture (eCAP) Module Reference Guide describes theenhanced capture module. It includes the module description and registers.
SPRUG05— TMS320x2833x, 2823x Enhanced Quadrature Encoder Pulse (eQEP) Reference Guidedescribes the eQEP module, which is used for interfacing with a linear or rotary incrementalencoder to get position, direction, and speed information from a rotating machine in highperformance motion and position control systems. It includes the module description and registers.
SPRUEU1— TMS320x2833x, 2823x Enhanced Controller Area Network (eCAN) Reference Guidedescribes the eCAN that uses established protocol to communicate serially with other controllers inelectrically noisy environments.
SPRUFZ5— TMS320F2833x, 2823x Serial Communication Interface (SCI) Reference Guide describesthe SCI, which is a two-wire asynchronous serial port, commonly known as a UART. The SCImodules support digital communications between the CPU and other asynchronous peripherals thatuse the standard non-return-to-zero (NRZ) format.
SPRUEU3— TMS320x2833x, 2823x Serial Peripheral Interface (SPI) Reference Guide describes the SPI- a high-speed synchronous serial input/output (I/O) port - that allows a serial bit stream ofprogrammed length (one to sixteen bits) to be shifted into and out of the device at a programmedbit-transfer rate.
SPRUG03— TMS320x2833x, 2823x Inter-Integrated Circuit (I2C) Reference Guide describes thefeatures and operation of the inter-integrated circuit (I2C) module.
Tools Guides—
SPRU513— TMS320C28x Assembly Language Tools User's Guide describes the assembly languagetools (assembler and other tools used to develop assembly language code), assembler directives,macros, common object file format, and symbolic debugging directives for the TMS320C28x device.
SPRU514— TMS320C28x Optimizing C Compiler User's Guide describes the TMS320C28x™ C/C++compiler. This compiler accepts ANSI standard C/C++ source code and produces TMS320 DSPassembly language source code for the TMS320C28x device.
SPRU608— The TMS320C28x Instruction Set Simulator Technical Overview describes the simulator,available within the Code Composer Studio for TMS320C2000 IDE, that simulates the instructionset of the C28x™ core.
SPRU625— TMS320C28x DSP/BIOS Application Programming Interface (API) Reference Guidedescribes development using DSP/BIOS.
SPRUG05A – August 2008 – Revised December 2008 Read This First 7Submit Documentation Feedback

1 Introduction
QEPA
QEPB
QEPI
Reference GuideSPRUG05A – August 2008 – Revised December 2008
Enhanced QEP (eQEP) Module
The enhanced quadrature encoder pulse (eQEP) module is used for direct interface with a linear or rotaryincremental encoder to get position, direction, and speed information from a rotating machine for use in ahigh-performance motion and position-control system.
A single track of slots patterns the periphery of an incremental encoder disk, as shown in Figure 1 . Theseslots create an alternating pattern of dark and light lines. The disk count is defined as the number ofdark/light line pairs that occur per revolution (lines per revolution). As a rule, a second track is added togenerate a signal that occurs once per revolution (index signal: QEPI), which can be used to indicate anabsolute position. Encoder manufacturers identify the index pulse using different terms such as index,marker, home position, and zero reference
Figure 1. Optical Encoder Disk
To derive direction information, the lines on the disk are read out by two different photo-elements that"look" at the disk pattern with a mechanical shift of 1/4 the pitch of a line pair between them. This shift isrealized with a reticle or mask that restricts the view of the photo-element to the desired part of the disklines. As the disk rotates, the two photo-elements generate signals that are shifted 90 out of phase fromeach other. These are commonly called the quadrature QEPA and QEPB signals. The clockwise directionfor most encoders is defined as the QEPA channel going positive before the QEPB channel and viseversa as shown in Figure 2 .
Enhanced QEP (eQEP) Module8 SPRUG05A – August 2008 – Revised December 2008Submit Documentation Feedback

T0
0 1 2 3 4 5 6 7 N−6 N−5 N−4 N−3 N−2 N−1 0
QEPA
QEPB
QEPI
Clockwise shaft rotation/forward movement
Anti-clockwise shaft rotation/reverse movement
0 N−1 N−2 N−3 N−4 N−5N−6 N−7 6 5 4 3 2 1 0 N−1 N−2
QEPA
QEPB
QEPI
T0
Legend: N = lines per revolution
T0
0.25T0±0.1T0
0.5T0±0.1T0
T0±0.5T0
QEPA
QEPB
QEPI
(gatedto
A and B)
QEPI
(gated to A)
QEPI
(ungated)
www.ti.com Introduction
Figure 2. QEP Encoder Output Signal for Forward/Reverse Movement
The encoder wheel typically makes one revolution for every revolution of the motor or the wheel may be ata geared rotation ratio with respect to the motor. Therefore, the frequency of the digital signal coming fromthe QEPA and QEPB outputs varies proportionally with the velocity of the motor. For example, a 2000-lineencoder directly coupled to a motor running at 5000 revolutions per minute (rpm) results in a frequency of166.6 KHz, so by measuring the frequency of either the QEPA or QEPB output, the processor candetermine the velocity of the motor.
Quadrature encoders from different manufacturers come with two forms of index pulse (gated index pulseor ungated index pulse) as shown in Figure 3 . A nonstandard form of index pulse is ungated. In theungated configuration, the index edges are not necessarily coincident with A and B signals. The gatedindex pulse is aligned to any of the four quadrature edges and width of the index pulse and can be equalto a quarter, half, or full period of the quadrature signal.
Figure 3. Index Pulse Example
SPRUG05A – August 2008 – Revised December 2008 Enhanced QEP (eQEP) Module 9Submit Documentation Feedback

v(k)[x(k)*x(k*1)
T+DX T
(1)
v(k)[X
t(k)*t(k*1)+X DT
(2)
2 Description
Description www.ti.com
Some typical applications of shaft encoders include robotics and even computer input in the form of amouse. Inside your mouse you can see where the mouse ball spins a pair of axles (a left/right, and anup/down axle). These axles are connected to optical shaft encoders that effectively tell the computer howfast and in what direction the mouse is moving.
General Issues: Estimating velocity from a digital position sensor is a cost-effective strategy in motorcontrol. Two different first order approximations for velocity may be written as:
where
v(k): Velocity at time instant k
x(k): Position at time instant k
x(k-1): Position at time instant k-1
T: Fixed unit time or inverse of velocity calculation rate
∆X: Incremental position movement in unit time
t(k): Time instant "k"
t(k-1): Time instant "k-1"
X: Fixed unit position
∆T: Incremental time elapsed for unit position movement.
Equation 1 is the conventional approach to velocity estimation and it requires a time base to provide unittime event for velocity calculation. Unit time is basically the inverse of the velocity calculation rate.
The encoder count (position) is read once during each unit time event. The quantity [x(k) - x(k-1)] isformed by subtracting the previous reading from the current reading. Then the velocity estimate iscomputed by multiplying by the known constant 1/T (where T is the constant time between unit timeevents and is known in advance).
Estimation based on Equation 1 has an inherent accuracy limit directly related to the resolution of theposition sensor and the unit time period T. For example, consider a 500-line per revolution quadratureencoder with a velocity calculation rate of 400 Hz. When used for position the quadrature encoder gives afour-fold increase in resolution, in this case, 2000 counts per revolution. The minimum rotation that can bedetected is therefore 0.0005 revolutions, which gives a velocity resolution of 12 rpm when sampled at 400Hz. While this resolution may be satisfactory at moderate or high speeds, e.g. 1% error at 1200 rpm, itwould clearly prove inadequate at low speeds. In fact, at speeds below 12 rpm, the speed estimate woulderroneously be zero much of the time.
At low speed, Equation 2 provides a more accurate approach. It requires a position sensor that outputs afixed interval pulse train, such as the aforementioned quadrature encoder. The width of each pulse isdefined by motor speed for a given sensor resolution. Equation 2 can be used to calculate motor speed bymeasuring the elapsed time between successive quadrature pulse edges. However, this method suffersfrom the opposite limitation, as does Equation 1 . A combination of relatively large motor speeds and highsensor resolution makes the time interval ∆T small, and thus more greatly influenced by the timerresolution. This can introduce considerable error into high-speed estimates.
For systems with a large speed range (that is, speed estimation is needed at both low and high speeds),one approach is to use Equation 2 at low speed and have the DSP software switch over to Equation 1when the motor speed rises above some specified threshold.
This section provides the eQEP inputs, memory map, and functional description.
10 Enhanced QEP (eQEP) Module SPRUG05A – August 2008 – Revised December 2008Submit Documentation Feedback