3-Axis Stepper Motor Controlww1.microchip.com/downloads/en/Appnotes/00003353A.pdfAN3353 3-Axis...

AN3353 3-Axis Stepper Motor Control Using an 8-Bit PIC®

Microcontroller

Introduction

Author: Maria Loida Canada, Microchip Technology Inc.

Three-axis control applications, such as on a CNC machine, robotics and dispensing machines, are widely used inthe industry. Most often, each motor has a dedicated controller that facilitates its speed control and sets its movementlimitations. The use of multiple controllers in the development of the control system implies a higher cost.

This project is created to develop a solution that can control up to three motors simultaneously. Utilizing a single PIC®

MCU with its Core Independent Peripherals (CIPs), driving the motors can be performed without additional burden tothe core. The developed cost-effective solution provides an accurate linear motor movement. The PIC® device can beused solely with the positions data embedded in its firmware or can be used as a slave for the applications requiringmore sophisticated control.

© 2020 Microchip Technology Inc. DS00003353A-page 1

Table of Contents

Introduction.....................................................................................................................................................1

1. Overview................................................................................................................................................. 3

2. Stepper Motor Control.............................................................................................................................4

2.1. Control Overview..........................................................................................................................42.2. Drive Circuit and Control Process................................................................................................ 52.3. 16-Bit High Resolution PWM for Control Signal...........................................................................62.4. Data Transfer................................................................................................................................6

3. Stepper Motor Control Characteristics.................................................................................................... 7

3.1. Torque Consideration................................................................................................................... 73.2. Stepping Rate...............................................................................................................................7

4. Step Mode Implementation..................................................................................................................... 8

4.1. Full-Step Drive..............................................................................................................................84.2. Half-Step Drive........................................................................................................................... 114.3. Microstepping.............................................................................................................................14

5. Firmware Flow Diagram........................................................................................................................ 16

6. 3-Axis Control Performance.................................................................................................................. 18

7. Conclusion............................................................................................................................................ 20

8. Appendix A: Schematics....................................................................................................................... 21

9. Appendix B: MPLAB® Code Configurator (MCC) Peripheral Initialization.............................................23

10. Appendix C: Source Code Listing......................................................................................................... 25

The Microchip Website.................................................................................................................................26

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Microchip Devices Code Protection Feature................................................................................................ 26

Legal Notice................................................................................................................................................. 26

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AN3353


1. OverviewThis application note describes a practical solution for controlling three motors independently. This application uses asingle PIC18F-Q43 device to control the drive signal being fed to the driver of stepper motors in 3-axes. With the useof a single 8-bit microcontroller, the implementation cost is substantially reduced.

This application has the following key features:

• Full-step, half-step, and microstepping (1/4 and 1/16) modes• Configurable steps/coordinate resolution• Speed and direction control of each motor• Up to three motors simultaneously controlled• Motor control using Core Independent Peripherals (CIPs)

The interconnection of peripherals to control the signals used for driving the motors is shown in Figure 1-1. The CIPsused in this design are the new 16-bit high-resolution PWM, Complementary Waveform Generator (CWG) and DirectMemory Access (DMA). The full-bridge driver is used for bipolar stepper motor control. The integration of on-chipperipherals like TMR0 and a conventional PWM with the firmware, enables the system to reliably perform 3-axiscontrol with minimum software overhead.

Figure 1-1. 3-Axis Motor Control Block Diagram

FULL BRIDGEDRIVER

(WINDING A)

FULL BRIDGEDRIVER

(WINDING B)

Winding B

Winding A

TMR0

I/O

PIC18FXXQ43

VMOTOR

FULL BRIDGEDRIVER

(WINDING A)

FULL BRIDGEDRIVER

(WINDING B)

I/O

Winding B

FULL BRIDGEDRIVER

(WINDING A)

I/O

FULL BRIDGEDRIVER

(WINDING B)

STEPPERMOTOR 3

STEPPERMOTOR 1

VMOTOR

FIRMWARE(Step Mode Selection,

Step Count, Stepping Algorithm)

CWG1

CWG3

PWM3

CWG2

PWM2

16-bit PWM3

16-bit PWM2

4

PWM1

Step RateGenerator

Winding B

Winding A

STEPPERMOTOR 2

16-bit PWM1

1.8°/Step

1.8°/Step

1.8°/Step

DMA Controller

4

4

MEMORY(PWM Modulation)

Note: For this application, Leadshine 42HS03 motors were used.

AN3353Overview


2. Stepper Motor ControlA stepper motor is a type of motor that rotates in discrete steps. It divides a full rotation into a number of equal stepsand moves through it, one at a time. It converts the input digital pulses into mechanical shaft rotation. It can be drivento rotate a specific number of steps and stop precisely when triggered to stop. For an in-depth discussion about thefundamentals of stepper motors, refer to AN907: Stepping Motors Fundamentals.

2.1 Control OverviewFigure 2-1 shows a block diagram of the generic system used for controlling the three stepper motors. TMR0 acts asa step rate generator, which is primarily responsible for controlling the speed of the motors. Every time the TMR0 rollsover, the stepping sequence in the firmware is loaded to the CWG and GPIO registers, while loading the PWM valuesthrough the DMA. Bipolar motor control circuit, which is composed of two H-bridge drivers, is used for driving eachmotor in a clockwise or counterclockwise direction. The drive signal for each motor is a combination of CWG andGPIO signals along with the 16-bit PWM output. Lastly, the firmware dictates the limitation of movement, dependingon the specified position.Figure 2-1. 3-Axis Motor Control Diagram

FIRMWARE(Stepping

Algorithm)

TMR0(Step Rate Generator)

PWM3

16-bit PWM3

16-bit PWM1

CWG3

16-bit PWM2

CWG1PWM1

CWG2PWM2

M1 H-BRIDGE DRIVER

(WINDING A)

M1 H-BRIDGE DRIVER

(WINDING B)

M2 H-BRIDGE DRIVER

(WINDING A)

M2 H-BRIDGE DRIVER

(WINDING B)

M3 H-BRIDGE DRIVER

(WINDING A)

M3 H-BRIDGE DRIVER

(WINDING B)

A

A’

A

A’

A

A’

B

B’

B

B’

B

B’

PROGRAM

MEMORY

I/O

I/O

I/O

DMA2

DMA3

DMA1

DMA4

DMA5

DMA6

Change in CWG1 Mode Signal



Current Modulation

Current Modulation

Current Modulation

Current Modulation

Current Modulation

Current Modulation

4

4

4

4

4

4

Change in drive signal mode



Drive CircuitsControl Signals

Data Transfer

AN3353Stepper Motor Control


http://ww1.microchip.com/downloads/en/Appnotes/00907a.pdf

2.2 Drive Circuit and Control ProcessThe rotating magnetic field and varying magnetic pole polarity (North/South) on the stator causes the rotor to spin.The magnetic field and magnetic polarity variation are produced by electrically energizing the two stepper motorwindings (Winding A and B). The energization is controlled by the CWG and PWM signals through the use of an H-bridge circuit. Figure 2-2 depicts the current flow through the half-bridge circuit during Forward and Reverse mode.The naming convention of Forward and Reverse mode are adopted from the modes of CWG and will be usedthroughout the document to indicate the state of Winding mode.

When Winding A is in Forward mode, the current is flowing through MOSFETs Q1 and Q4 down to ground, whileensuring that Q2 and Q3 are OFF. Otherwise, when it operates in Reverse mode, the current flows through Q2 andQ3, while keeping Q1 and Q4 OFF. The same principle applies to the MOSFETs Q5, Q6, Q7 and Q8 on Winding B.The switching of the MOSFETs in Winding B is implemented through the use of CWG Forward and Reverse-FullBridge modes, while the MOSFETs in Winding A are controlled by GPIO output and 16-bit PWM. Thus, the drivemethod for each motor is a combination of firmware and peripheral drive, to assure that all the motors are exposed tosimilar control factors. Refer to TB3118: Complementary Waveform Generator, for more details about the CWGperipheral. For the drive circuits used, refer to section Appendix A: Circuit Schematics.Figure 2-2. Drive Circuits and Control Signals

Vmotor

Winding AA A’

Q1

Q2

Q3

Q4

LATxy1

LATxy2(16-bit PWM)

LATxy3

LATxy4(16-bit PWM)

Vmotor

Winding BB B’

Q5

Q6

Q7

Q8

CWGxA

CWGxB

CWGxC

CWGxD

FORWARD MODE REVERSE MODE



http://ww1.microchip.com/downloads/en/appnotes/90003118a.pdf

2.3 16-Bit High Resolution PWM for Control SignalThe 16-bit Pulse-Width Modulator can produce a high-resolution modulation at low frequency. In this application, thedrive resolution will be mainly determined by the step mode implementation. The switching frequency must be highenough to operate beyond the audio frequency. The arrangement was made by choosing the PWM to operate in 10-bit, having a 62.5 kHz switching frequency, which is within the range of typical driver switching frequency.

The 16-bit PWM is used for driving the low-side MOSFETs of Winding A for all motors. It is connected to both low-side MOSFETs through Peripheral Pin Select (PPS), but it is never intended to turn on both sides simultaneously.The 16-bit PWM has an independent 16-bit period timer, which is chosen to be HFINTOSC or equivalent to 64 MHzin this application. The PWMOUT is in Left-Aligned mode. For proper PWM operation, the registers PWMxPR andPWMxSaP1 must be properly configured. The requested frequency can be attained by setting up the PWMxPRregister. The value of this register is equivalent to the number of PWM clock periods in the PWM period or it can beexpressed as shown in Equation 2-1.

The PWMxSaP1 register determines the active period of slice “a”, parameter 1 output. The duty cycle shown in Equation 2-2 can then be calculated by getting the ratio of PWMxSaP1 to the PWMxPR value.

The automatic loading of the PWMxSaP1 register is enabled through setting the respective DMAx as the auto-loadtrigger source in the PWMxLDS register. For more information about the 16-bit PWM, refer to the device data sheet.Equation 2-1. PWM Period Register Value�� = �� Equation 2-2. Duty Cycle Calculation�� = ��1�� × 100%

2.4 Data TransferThe Look-Up Table of modulation values is initially stored in Programmable Flash Memory. The DMA is utilized fortransferring the modulation values to PWM registers without the CPU intervention, freeing up the core for doing othertasks. DMA1 is used for transferring the values from the program memory to the Slice 1 Output of 16-bit PWM1defined by the PWM1S1P1L and PWM1S1P1H registers, illustrated in Figure 2-1, while DMA2 is used for passing onthe modulation data from the program memory to the conventional PWM1 registers: CCPR1L and CCPR1H. EachDMA channel is tied to its specific PWM peripheral to ensure that the transfer will simultaneously take placewhenever a transfer trigger is received.

All the DMA channels are configured to start the data transfer when TMR0 interrupt is triggered. The TMR0 isselected as a trigger for starting the data transfer through the DMAnSIRQ (DMA Start Interrupt Request SourceSelection) register. But for the interrupt source to take effect, the SIRQEN (Start of Transfer Interrupt RequestEnable) register of each DMA must be enabled.

This application provides a drive implementation in 1/4 and 1/16 microstepping. It is important to note that the arraysize of PWM modulation values for 1/4 and 1/16 microstepping are different and the respective DMA source sizeregister must be correctly initialized to transfer all the data necessary to complete a full step. Since the DMA isoperating in 8-bit, the DMA source size must be equivalent to twice the number of array elements. For 1/4microstepping, the step resolution is 16, which means that the DMA source size register must be equivalent to 32 or0x20; and for 1/16 microstepping with step resolution of 64 the DMA source size must be 128 or 0x80. To learn moreinformation about DMA, refer to TB3164: Direct Memory Access on 8-bit PIC® Microcontrollers and refer to the devicedata sheet for proper peripheral configuration.



http://ww1.microchip.com/downloads/en/AppNotes/TB3164-Direct%20Memory-Access-on-8-bit-PIC-MCU-DS90003164B.pdf

3. Stepper Motor Control CharacteristicsFor proper operation, stepper motor characteristics must be carefully considered. Characteristics to consider aretorque, speed and stepping rate. This section discusses about how these characteristics affect the steppingimplementation.

3.1 Torque ConsiderationStepper motor maintains torque at relatively low speed. The torque required to move the load must be met by thestepper motor specifications. Stepping motor manufacturers will specify several torques in their data sheets for theirmotors. The torque magnitude depends on the driving technique, stepping rate, and winding current.

3.2 Stepping RateStep rate refers to the speed at which the hardware-firmware combination can send step pulses to the stepper motordriver. It is expressed in PPS (Pulse Per Second) and dictates the speed of the motor. To know more about how it isimplemented using a PIC microcontroller, refer to the Stepping Rate section of AN2326: High-Torque/High PowerBipolar Stepper Motor using 8-bit PIC® MCUs.

AN3353Stepper Motor Control Characteristics


http://ww1.microchip.com/downloads/en/AppNotes/00002326A.pdfhttp://ww1.microchip.com/downloads/en/AppNotes/00002326A.pdf

4. Step Mode ImplementationStep mode is a drive technique used to rotate a stepper motor. It indicates the magnitude of a step angle taken inevery energization of the stator windings. Each mode has a corresponding stepping resolution and output torque. Thestep modes that can be implemented in 3-axis control using a PIC18F-Q43 microcontroller are:

• Full-step Drive• Half-step Drive• Microstepping Drive (1/4 and 1/16)

The step mode implementation used in this application is referenced in AN2326: High-Torque/High Power BipolarStepper Motor using 8-bit PIC® MCUs. The principle of the stepping mode used is the same, only the actualimplementation using the PIC18FXXQ43 device will be shown here. Likewise, the implementation is applicable to allthree motors in 3-axis.

4.1 Full-Step DriveOn this drive, two phases are energized at the same time. The drive circuit implementation is shown in Figure 4-1.The CWG controls the Winding B while the Winding A is controlled by toggling the output of GPIO depending onstepping algorithm. Meanwhile, Figure 4-2 illustrates the algorithm used for stepping the motor. The individual outputstate of each pin is shown to properly move the shaft’s position into its equivalent full-step angle.

Figure 4-3 shows the firmware execution used in controlling the signals. Every time the TMR0 interrupt is triggered,stepCounter variables are incremented. stepCounter signifies that the specific mode used is full-step and resetsto 0 whenever it reaches 4. stepCounter2Mx are compared to their corresponding MxdesiredStep. If the counterexceeds the desired step, the motor will be stopped and axis_movementDone will be set. The definition of theaxis can be x, y or z, depending on the specific motor movement it resembles. After all theaxis_movementDone are set, the TMR0 is disabled to make sure that it will not count and to avoid an interrupt to beimproperly triggered. All the stepCounter2Mx are cleared to ensure that the counting for the succeeding positionsbegins at zero. The movementDone variable is used in the main program to determine if all the motor movementsare finished and gives the signal to prepare the system for another movement.

The switch case determined by the motorDir variable decides on which direction the motors will rotate. The motorsare designed to be driven simultaneously, so at every Interrupt event, the motorDir will command which case toexecute. Each case contains the direction of the motors and all the motors that used the drive table for clockwise andcounterclockwise direction. The drive table requires a specific set of IO and CWG for each motor.

Figure 4-1. Full-Step Drive

H-Bridge

H-BridgeCWGx

LATxy1

LATxy2

LATxy3

LATxy4

H-Bridge

H-BridgeCWGx

LATxy1

LATxy2

LATxy3

LATxy4

AN3353Step Mode Implementation


http://ww1.microchip.com/downloads/en/AppNotes/00002326A.pdfhttp://ww1.microchip.com/downloads/en/AppNotes/00002326A.pdf

Figure 4-2. Full-Step Drive Stepping Algorithm in Clockwise Direction

Q1LATxy1

Q2 LATxy2

Q3 LATxy3

Q4 LATxy4

Q5 CWGxA

Q6 CWGxB

Q7 CWGxC

Q8 CWGxD

Win

din

g A

CWG Drive

STEP 1 STEP 2 STEP 3 STEP 4 STEP 1 STEP 2 STEP 3

Forward Forward ReverseReverse Forward Forward ReverseReverse

Win

din

g B

Forward Reverse ForwardReverse Forward Reverse ForwardReverseWindingMode



Figure 4-3. Full-Step Drive Stepping Algorithm Flowchart

Step_One: LATxbits.LATxy1 = 0TRISxbits.TRISxy2 = 0LATxbits.LATxy3 = 1TRISxbits.TRISxy4 = 1CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Two: LATxbits.LATxy1 = 1TRISxbits.TRISxy2 = 1LATxbits.LATxy3 = 0TRISxbits.TRISxy4 = 0CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Three: LATxbits.LATxy1 = 1TRISxbits.TRISxy2 = 1LATxbits.LATxy3 = 0TRISxbits.TRISxy4 = 0CWGxCON0bits.MODE0 = 0 (Forward)

Step_Four: LATxbits.LATxy1 = 0TRISxbits.TRISxy2 = 0LATxbits.LATxy3 = 1TRISxbits.TRISxy4 = 1CWGxCON0bits.MODE0 = 0 (Forward)

FULL STEP DRIVE TABLE CLOCKWISE DIRECTION

Step_One: LATxbits.LATxy1 = 1TRISxbits.TRISxy2 = 1LATxbits.LATxy3 = 0TRISxbits.TRISxy4 = 0CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Two: LATxbits.LATxy1 = 0TRISxbits.TRISxy2 = 0LATxbits.LATxy3 = 1TRISxbits.TRISxy4 = 1CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Three: LATxbits.LATxy1 = 0TRISxbits.TRISxy2 = 0LATxbits.LATxy3 = 1TRISxbits.TRISxy4 = 1CWGxCON0bits.MODE0 = 0 (Forward)

Step_Four: LATxbits.LATxy1 = 1TRISxbits.TRISxy2 = 1LATxbits.LATxy3 = 0TRISxbits.TRISxy4 = 0CWGxCON0bits.MODE0 = 0 (Forward)

FULL STEP DRIVE TABLE COUNTERCLOCKWISE DIRECTION

TMR0 Interrupt

stepCounter2M1 > M1desiredStep?

stepCounter2M1 = 0;M1stop();

x_movementDone = 1;

YES

NO



y_movementDone = 1;

YES

NO



z_movementDone = 1;

YES

NOstepCounter == 4?

stepCounter++;stepCounter2M1++;stepCounter2M2++;stepCounter2M3++;

Return

Clear stepCounterYES

NO

x_movementDone && y_movementDone && z_movementDone?

case 0: M1CWFull(); M2CWFull(); M3CWFull(); case 1: M1CCWFull(); M2CWFull(); M3CWFull(); case 2: M1CWFull(); M2CCWFull(); M3CWFull(); case 3: M1CCWFull(); M2CCWFull(); M3CWFull(); case 4: M1CWFull(); M2CWFull(); M3CCWFull(); case 5: M1CCWFull(); M2CWFull(); M3CCWFull(); case 6: M1CWFull(); M2CCWFull(); M3CCWFull(); case 7: M1CCWFull(); M2CCWFull(); M3CCWFull();

switch motorDir

TMR0_StopTimer(); stepCounter2M1 = 0;stepCounter2M2 = 0;stepCounter2M3 = 0;movementDone = 1;

YES

NO

NO



4.2 Half-Step DriveHalf-step drive alternates between two phases on and a single phase on. It increases the resolution of the angle byhalving the basic step angle, thus causing a smoother rotation than full-step. Figure 4-4 shows the drive circuitimplementation with the control signals coming from CWG and GPIO output. While, Figure 4-5 illustrates the steppingalgorithm used in this drive technique.

Figure 4-6 shows the firmware execution similar to the firmware flow in Figure 4-3. The value of the stepCounterdoubled, which clearly states that the algorithm used is twice as long as the full-step algorithm. The drive table inclockwise and counterclockwise direction for all the steps are also shown.Figure 4-4. Half-Step Drive Circuit

H-Bridge

H-BridgeCWGx

H-Bridge

H-BridgeCWGx

H-Bridge

H-BridgeCWGx

H-Bridge

H-BridgeCWGx

STEP 1 STEP 2

STEP 3 STEP 4

LATxy1

LATxy2

LATxy3

LATxy4

LATxy1

LATxy2

LATxy3

LATxy4

LATxy1

LATxy2

LATxy3

LATxy4

LATxy1

LATxy2

LATxy3

LATxy4



Figure 4-5. Half-Step Drive Stepping Algorithm

Q1LATxy1

Q2 LATxy2

Q3 LATxy3

Q4 LATxy4

Q5 CWGxA

Q6 CWGxB

Q7 CWGxC

Q8 CWGxD

Win

din

g A

CWG Drive

STEP 1 STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 STEP 7

OFF Forward ForwardForward OFF Reverse ReverseReverse

Win

din

g B

WindingMode

Forward Forward ReverseOFF Reverse Reverse ForwardOFF

STEP 8 STEP 1 STEP 2

ForwardForward

ForwardOFF



Figure 4-6. Half-Step Drive Firmware Execution

TMR0 Interrupt



x_movementDone = 1;

YES

NO



y_movementDone = 1;

YES

NO



z_movementDone = 1;

YES

NO

stepCounter == 8?

stepCounter++;stepCounter2M1++;stepCounter2M2++;stepCounter2M3++;

Return

Clear stepCounterYES

NO

case 0: M1CWHalf(); M2CWHalf(); M3CWHalf(); case 1: M1CCWHalf(); M2CWHalf(); M3CWHalf(); case 2: M1CWHalf(); M2CCWHalf(); M3CWHalf(); case 3: M1CCWHalf(); M2CCWHalf(); M3CWHalf(); case 4: M1CWHalf(); M2CWHalf(); M3CCWHalf(); case 5: M1CCWHalf(); M2CWHalf(); M3CCWHalf(); case 6: M1CWHalf(); M2CCWHalf(); M3CCWHalf(); case 7: M1CCWHalf(); M2CCWHalf(); M3CCWHalf();

switch motorDir

Step_One: LATxbits.LATxy1 = 1 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 0 CWGxCON0bits.EN = 0 (OFF)

Step_Two: LATxbits.LATxy1 = 1 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 0 CWGxCON0bits.MODE0 = 0 (Forward)

Step_Three: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 0 (Forward)

Step_Four: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 0 LATxbits.LATxy3 = 1 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 0 (Forward)

HALF STEP DRIVE TABLE CLOCKWISE DIRECTION

Step_Five: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 0 LATxbits.LATxy3 = 1 TRISxbits.TRISxy4 = 1 CWGxCON0bits.EN =0 (OFF)

Step_Six: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 0 LATxbits.LATxy3 = 1 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Seven: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Eight: LATxbits.LATxy1 = 1 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 0 CWGxCON0bits.MODE0 = 1 (Reverse)

Step_One: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 0 LATxbits.LATxy3 = 1 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 0 (Forward)

Step_Two: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 0 (Forward)

Step_Three: LATxbits.LATxy1 = 1 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 0

TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 0 CWGxCON0bits.EN = 0 (OFF)

HALF STEP DRIVE TABLE COUNTERCLOCKWISE DIRECTION

Step_Five: LATxbits.LATxy1 = 1 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 0 CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Six: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 1 LATxbits.LATxy3 = 0 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Seven: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 0 LATxbits.LATxy3 = 1 TRISxbits.TRISxy4 = 1 CWGxCON0bits.MODE0 = 1 (Reverse)

Step_Eight: LATxbits.LATxy1 = 0 TRISxbits.TRISxy2 = 0 LATxbits.LATxy3 = 1 TRISxbits.TRISxy4 = 1 CWGxCON0bits.EN = 0 (OFF)

x_movementDone && y_movementDone && z_movementDone?

TMR0_StopTimer(); stepCounter2M1 = 0;stepCounter2M2 = 0;stepCounter2M3 = 0;movementDone = 1;

YES

NO

CWGxCON0bits.MODE0 = 0 (Forward) Step_Four: LATxbits.LATxy1 = 1



4.3 MicrosteppingMicrostepping is a manner of moving the stator flux of a stepper motor smoothly. One type of microstepping isconstant-torque, which is used in this application. Constant-torque microstepping is achieved by simultaneouslyvarying the current in both windings of a stepper motor.

The drive circuit used in this stepping mode is identical to the full-step and half-step circuits. However, the controlsignals are modulated instead of supplying a full-on or full-off signals. The currents can be varied by changing thePWM percent modulation in accordance with the Equation 4-1 and Equation 4-2.Equation 4-1. Winding A Current Formula�� = �� × sin �� × 360�� Equation 4-2. Winding B Current Formula�� = �� × cos �� × 360�� Using the 1/16 microstepping, assume that IMAX is equivalent to one and the drive is in step number one. The sin of360° multiplied by the present step number divided by 64 (1/16 microstepping resolution) results to 0.098. Thisrepresents that the modulation of current in Winding A must only be 9.8% of the maximum current. The modulation ofWinding A and Winding B for the remaining 63 steps is calculated and plotted in Figure 4-7. The step resolution of 64makes the torque graph resemble a sinusoid. The stepping algorithm used in 1/16 microstepping is shown on Figure4-8.Figure 4-7. Phase Diagram and Torque Response of Constant Torque 1/16 Microstepping

STEP 64(0% IA,

100% IB)

IA(%)

IB(%)

STEP 16(100% IA,

0% IB)

STEP 48(-100% IA,

0%IB)

Winding ATorque

Winding BTorque



Figure 4-8. Constant-Torque Microstepping Drive Signal

Q1LATxy1

Q2 PWMx

Q3 LATxy3

Q4 PWMx

Q5 CWGxA

Q6 CWGxB

Q7 CWGxC

Q8 CWGxD

Win

din

g A

CWG Drive

STEPSW

ind

ing

B

WindingMode

ForwardModulated

OFF ReverseModulated

Reverse OFFReverseModulated

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64

ForwardModulated

Forward

OFF ReverseModulated

ReverseModulated

OFFReverse ForwardForwardModulated

ForwardModulated



5. Firmware Flow DiagramThis section explains the firmware design implemented for successfully driving the three motors in 3-axis.Figure 5-1. Firmware Flowchart

START

System_Initialize();

FeedingData();

SetPosition();

positionSet = 0;positionSet?

Motor_Driver();

Interrupt Initialize

dataFeedDone? dataFeedDone = 0;

StartMotorDrive();

positionSet?

movementDone? __delay_ms(15); startDataFeed = 1;

YES

YES

YES

NO

NO

NO

Motor_Driver();

//Pick one type of drive// Full_Setup();// Half_Setup();// Microstep4_Setup(); Microstep16_Setup();

EXIT

FeedingData();

startDataFeed?

startDataFeed = 0;

coordInd++;x_coordinate = x_position[coordInd]; y_coordinate = y_position[coordInd]; z_coordinate = z_position[coordInd];

x_buffer = x_coordinate;y_buffer = y_coordinate;z_buffer = z_coordinate;

coordInd > max?

StopMotorDrive();

EXIT

YES

NO

YES

NO

dataFeedDone = 1;

The firmware flow starts with the SYSTEM_Initialize() routine. This routine initializes pin configuration, oscillatorand all the peripherals used in the application. It is followed by enabling interrupts to address the functions requiringinterrupts. The Motor_Driver() function contains the different drive implementation. Pick one type of drive-byuncommenting the function of the chosen drive. The selected drive will assign the value ofstepping_mode_constant, which will be used for calculating the number of steps required to rotate in a distinctposition. Notice that the type of drive will only be setup once at the beginning of the program, and the type of drivethat will be used will depend on the application requirement and user’s discretion.

After all the initialization is done, the program will undergo a continuous loop, executing the functions necessary tosuccessfully move the motors in predefined positions. The FeedingData() function contains the commands foracquiring and processing the desired position. The positions initialized at the beginning of the program are placed inthe axis_coordinate parameters for later processing. The condition that tests coordInd against max variabletells if the end position has been reached and signifies that the motors will be stopped if the condition is satisfied.Otherwise, the dataFeedDone variable will be set to be used as a test variable for the next instruction.When the dataFeedDone test variable is satisfied, the SetPosition() function will be executed. This functionserves a vital role in the 3-axis motion control. This function consists of checking if the individual motor movementsare completed through testing the axis_movementDone variable. Provided that the previous movement is finished,the current axes coordinate will be tested against the previous axes coordinate. If the current and previouscoordinates are not equal, two conditional statements will be tested consequently. The first condition tests if thecurrent coordinate is less than the previous coordinate; if so, the resulting current coordinate will be the previous

AN3353Firmware Flow Diagram


coordinate less the current coordinate shown in Equation 5-1. The Mxdirection is set to the counterclockwisedirection and the DMA is initialized for transferring the modulation data necessary for moving in the counterclockwisedirection. However, if the current coordinate is greater than the previous coordinate, the resulting current coordinatewill be the current coordinate less the previous coordinate, as shown in Equation 5-2. Furthermore, theMxdirection will be set to the clockwise direction and the DMA source is initialized to transfer the modulation datafor clockwise direction.

The resulting current coordinate will be used to compute for the motor’s desired step, which is shown in Equation 5-3.The constant variable STEPS_PER_COORDINATE may take any value, depending on the tool used for convertingrotational to linear motion. This variable is introduced for flexibility in the application. The meaning of axis inaxis_coordinate can be x, y or z, depending on the coordinate, and the x in MxDesiredStep can be 1, 2 or 3,depending on the motor number. The pairs created in this control scheme are as follows: x_coordinate to M1,y_coordinate to M2 and z_coordinate to M3.Equation 5-1. axis_coordinate < axis_prevCoordinate�� = ��− ��Equation 5-2. axis_coordinate > axis_prevCoordinate�� = ��− ��Equation 5-3. Motor Desired Step�� = ��_�� × ��_��_�� × ��_��_�� Subsequently, the previous coordinate equates to the current coordinate to be the reference for successive positions.Then, the motor drive is enabled by clearing the auto-shutdown feature of CWG and setting the drive pins as output.The positionSet variable is set, which primarily indicates that the setting of position is done.Consequently, the function StartMotorDrive() will be implemented, which literally starts the drive of the threemotors. The testing of movementDone variable implies that all the motors must be moved to their destination beforefeeding the next sets of data for the subsequent movements. The loop will be continually running, executing the tasksmentioned above until coordinate movements were completed. Refer to section Appendix C: Source Code Listing forthe complete source code.

AN3353Firmware Flow Diagram


6. 3-Axis Control PerformanceIn order to show that the microcontroller can provide drive signals simultaneously, a logic analyzer is used to capturethe drive signal when operating in different stepping modes.

Figure 6-1. Drive Signals for Three Motors from MCU Captured using Logic Analyzer

A. Full-Step B. Half-Step

C. ¼ Microstepping D. 1/16 Microstepping

M1WA

M1WB

M2WA

M2WB

M3WA

M3WB

M1WA

M1WB

M2WA

M2WB

M3WA

M3WB

M1WA

M1WB

M2WA

M2WB

M3WA

M3WB

M1WA

M1WB

M2WA

M2WB

M3WA

M3WB

LEGEND:M1WA – Motor 1 Winding AM1WB – Motor 1 Winding BM2WA – Motor 2 Winding A

M2WB – Motor 2 Winding BM3WA – Motor 3 Winding AM3WB – Motor 3 Winding B

Figure 6-2. Drive Signal Step Mode Comparison

A. Full-Step B. Half-Step

C. ¼ Microstepping C. 1/16 Microstepping

MxWA

MxWB

MxWAAnalog Signal

MxWBAnalog Signal

MxWA

MxWB

MxWAAnalog Signal

MxWBAnalog Signal

MxWA

MxWB

MxWAAnalog Signal

MxWBAnalog Signal

MxWA

MxWB

MxWAAnalog Signal

MxWBAnalog Signal

Figure 6-3. Data Coordinates Feed to the Motor

AN33533-Axis Control Performance


Figure 6-1 shows the movement of motors in 3-axis in terms of number of steps driven at full-step, half-step andmicrostepping (1/4 and 1/16) with the speed of 180 RPM. It can be observed that the time elapsed for all step modeimplementations is uniform because they all operate at 180 RPM. But, it can be seen in Figure 6-2 that the requiredPPS (Pulse per Second) for each drive is different to retain the speed of 180 RPM. The drive signals shown are fromthe control signals of low-side MOSFETs of bipolar drive circuits.

An example is shown in Figure 6-3, in which the positions are defined as an array of coordinates. At an instance, thepositions having the same element order for all the axis will be processed by the firmware using Equations 5-1 or 5-2depending on the preceding coordinate before passing onto Equation 5-3. Table 6-1 shows the data of how thedesired steps are calculated for all the motors with STEPS_PER_COORDINATE of 100, based on the coordinate givenin Figure 6-3.Table 6-1. Step Calculation for Three Motors in Full-Step Mode

n Xn |Xn+1 - Xn| M1desiredStep Yn |Yn+1 - Yn| M2desiredStep Zn |Zn+1 - Zn| M3desiredStep

0 0 0 0

1 3 3(CW) 300 11 11(CW) 1100 5 5(CW) 500

2 12 9(CW) 900 8 3(CCW) 300 3 2(CCW) 200

3 8 4(CCW) 400 12 4(CW) 400 9 6(CW) 600

4 2 6(CCW) 600 5 7(CCW) 700 2 7(CCW) 700

AN33533-Axis Control Performance


7. ConclusionPIC18F-Q43 devices have the capacity to provide control signals for 3-axis stepper motor control. Aside fromproviding control signals, it is also capable of setting the movement limitation to accurately move the motors to thedefined positions. Different modes of stepping drive such as full-step, half-step, 1/4 and 1/16 microstepping can beimplemented to achieve the desired resolution. The CIPs such as CWG, 16-bit PWM and DMA significantly reducedthe burden on the core, enabling the CPU to process data for motor control movements.

AN3353Conclusion


8. Appendix A: SchematicsFigure 8-1. Circuit Schematics

POWER

R4510kΩ

8

12

7

5

34

6

R4610kΩ

12

DC+

R4710kΩ

8

12

7

5

34

6

R4810kΩ

R30100mΩ

M1WA1

M1WA2

M1WA2

BHOM1WA

BLOM1WA

ALOM1WA

AHOM1WA

SHUNT_M1WA

FDS3992

FDS3992

FDS3992

FDS3992

IC20

IC20

IC23

IC23

J13811‐S1‐002‐10‐017101

Motor 1 Drive Circuit PIC18FxxQ

43

RA0RA1RA2RA3RA4RA5RE0

RB7RB6RB5RB4RB3RB2RB1RB0

RE1RE2VDDAVSSRA7RA6

AVDDVSSRD7RD6RD5RD4

CWG3B

RC0RC1RC2RC3RD0RD1

RC7RC6RC5RC4RD3RD2

123456789

10

11

12

13

14

15

16

17

18

19

20

40

39

38

37

36

35

34

33

32

31

30

29

28

27

26

25

24

23

22

21

CWG3CCWG3DLATA3

LATB7PWM1CWG1ACWG1CCWG1DCWG1BPWM1LATB0

PWM3PWM2PWM2

PWM3CWG2D

LATA4

LATE0LATE1

CWG2ACWG3A

CWG2BCWG2C

87654321

910111213

16

1415

BHOBHSBLOVSSVDDALOAHS

BHBENBHIBLIALIAHINC

AHBAHO

BHOM1WBBHSM1WBBLOM1WB

AGNDVDDM1WBALOM1WBAHSM1WBAHOM1WB

BHBM1WB+5V

AHBM1WB

MIC4606

IC16

12

C200.1µF

C190.1µF

+15V

J27811‐S1‐002‐10‐017101

VDDM1WB

C91µF

C101µF

CWG1DCWG1C

CWG1BCWG1A

910111213

16

1415

PWM1

BHBENBHIBLIALIAHINC

BHOBHSBLOVSSVDDALOAHSAHOAHB

BHOM1WABHSM1WABLOM1WAAGND

VDDM1WAALOM1WAAHSM1WAAHOM1WA

BHBM1WA+5V

LATB7

PWM1LATB0

AHBM1WA

MIC4606

87654321

IC15

C71µF

C81µF

12

C180.1µF

C170.1µF

+15V

J21811‐S1‐002‐10‐017101

VDDM1WA

R4910kΩ

8

12

7

5

34

6

R5010kΩ

12

DC+

R5110kΩ

8

12

7

5

34

6

R5210kΩ

R104100mΩ

M1WB1

M1WB2

M1WB2

BHOM1WB

BLOM1WB

ALOM1WB

AHOM1WB

SHUNT_M1WB

FDS3992

FDS3992

FDS3992

FDS3992

IC22

IC22

IC24

IC24

J14811‐S1‐002‐10‐017101

1 32

IN

GND_NO PAD GND_TAB

OUT IN

GROUND_1

OUT

GROUND_2

12

12

12

12

RAPC722X

J2C29100µF

C210.1µF

IC19MC7815CD2TG

C280.1µF

C447µF

J1811‐S1‐002‐10‐017101

J10811‐S1‐002‐10‐017101

J11811‐S1‐002‐10‐017101

J12811‐S1‐002‐10‐017101

IC21MC7805CDTG

C3647µF

C370.1µF

R271kΩ

LED15SML‐D12Y1WT86

R401Ω

C450.1µF

C46100µF

TP15014

TP25014

TP235014

+15V +5V AVDD

C3470µF

C300.1µF

R260Ω

DC+

Microcontroller

+5V

MCLR

AN3353Appendix A: Schematics


Figure 8-2. Motor 2 and 3 Drive Circuit Schematics

R6110kΩ

8

12

7

5

34

6

R6210kΩ

12

DC+

R6310kΩ

8

12

7

5

34

6

R6410kΩ

R32100mΩ

M3WA1

M3WA2

M3WA2

BHOM3WA

BLOM3WA

ALOM3WA

AHOM3WA

SHUNT_M3WA

FDS3992

FDS3992

FDS3992

FDS3992

IC31

IC31

IC32

IC32

J17811‐S1‐002‐10‐017101

Motor 3 Drive Circuit

87654321

910111213

16

1415


BHBENBHIBLIALIAHINC

AHBAHO



BHBM3WB+5V

AHBM3WB

MIC4606

IC30

12

C340.1µF

C330.1µF

+15VJ31

811‐S1‐002‐10‐017101

VDDM3WB

C311µF

C321µF

CWG3DCWG3C

CWG3BCWG3A

910111213

16

1415

BHBENBHIBLIALIAHINC


BHOM3WABHSM3WABLOM3WAAGNDVDDM3WAALOM3WAAHSM3WAAHOM3WA

BHBM3WA+5V

AHBM3WA

MIC4606

87654321

IC29

C151µF

C161µF

12

C270.1µF

C260.1µF

+15VJ30

811‐S1‐002‐10‐017101

VDDM3WA

PWM3LATA4

PWM3LATA3

R5310kΩ

8

12

7

5

34

6

R5410kΩ

12

DC+

R5510kΩ

8

12

7

5

34

6

R5610kΩ

R31100mΩ

M2WA1

M2WA2

M2WA2

BHOM2WA

BLOM2WA

ALOM2WA

AHOM2WA

SHUNT_M2WA

FDS3992

FDS3992

FDS3992

FDS3992

IC25

IC25

IC26

IC26

J15811‐S1‐002‐10‐017101

Motor 2 Drive Circuit

87654321

910111213

16

1415


BHBENBHIBLIALIAHINC

AHBAHO



BHBM2WB+5V

AHBM2WB

MIC4606

IC18

12

C250.1µF

C240.1µF

+15VJ28

811‐S1‐002‐10‐017101

VDDM2WB

C111µF

C111µF

CWG2DCWG2C

CWG2BCWG2A9

10111213

16

1415BHBEN

BHIBLIALIAHINC


BHOM2WABHSM2WABLOM2WAAGNDVDDM2WAALOM2WAAHSM2WAAHOM2WB

BHBM2WA+5V

AHBM2WA

MIC4606

87654321

IC17

C111µF

C481µF

12

C230.1µF

C220.1µF

+15VJ29

811‐S1‐002‐10‐017101

VDDM2WA

PWM2LATE1

PWM2LATE0

R5710kΩ

8

12

7

5

34

6

R5810kΩ

12

DC+

R5910kΩ

8

12

7

5

34

6

R6010kΩ

R105100mΩ

M2WB1

M2WB2

M2WB2

BHOM2WB

BLOM2WB

ALOM2WB

AHOM2WB

SHUNT_M2WB

FDS3992

FDS3992

FDS3992

FDS3992

IC27

IC27

IC28

IC28

J16811‐S1‐002‐10‐017101

R6510kΩ

8

12

7

5

34

6

R6610kΩ

12

DC+

R6710kΩ

8

12

7

5

34

6

R6810kΩ

R106100mΩ

M3WB1

M3WB2

M3WB2

BHOM3WB

BLOM3WB

ALOM3WB

AHOM3WB

SHUNT_M3WB

FDS3992

FDS3992

FDS3992

FDS3992

IC33

IC33

IC34

IC34

J18811‐S1‐002‐10‐017101

STEPPERMOTOR 1

M1WA1

M1WA2

M1WB1

M1WB2

STEPPERMOTOR 2

M2WA1

M2WA2

M2WB1

M2WB2

STEPPERMOTOR 3

M3WA1

M3WA2

M3WB1

M3WB2

Winding A

Winding B

Winding A

Winding B

Winding A

Winding B

AN3353Appendix A: Schematics


9. Appendix B: MPLAB® Code Configurator (MCC) PeripheralInitializationMPLAB® Code Configurator (MCC) is an easy-to-use plugin tool for MPLAB® X IDE that generates codes forcontrolling the peripherals of Microchip microcontrollers, based on the settings made in its Graphical User Interface(GUI). MCC is utilized to easily configure the peripherals used in this motor control application. Refer to the MPLAB®

Code Configurator User’s Guide (DS40001725) for further information on how to install and set up the MCC inMPLAB® X IDE.

The step-by-step process of using MCC in this application is listed below.

1. In the system module, set the clock to HFINTOSC with the highest available frequency of 64 MHz.2. Timer2 is used as a clock source for CCP1/2/3. For the CCP to produce PWM, the Timer2 clock source must

be set to FOSC/4. Enable the Timer.3. Configure the Timer0 in 16-bit Timer mode with MFINTOSC clock source, having a requested period of 1.5 ms.

Enable the Timer interrupt and let the Timer0 be initially disabled.4. For Motor 1 drive, configure PWM1, CCP1, CWG1, DMA Channel 1 and DMA Channel 2.

4.1. Set up the PWM1 with HFINTOSC clock source, having a requested frequency of 62.5 kHz and dutycycle of 50%. Enable the PWM module.

4.2. CCP1 module must be in PWM mode with Timer2 as the selected Timer, having a duty cycle of 50%.4.3. CWG1 must be configured with CCP1_OUT as an input source, with Output mode in Forward Full-

Bridge mode and HFINTOSC as the selected clock source. Enable CWG1.5. For Motor 2 drive, configure PWM2, CCP2, CWG2, DMA Channel 3 and DMA Channel 4.



Bridge mode and HFINTOSC as the selected clock source. Enable CWG2.6. For Motor 3 drive, configure PWM3, CCP3, CWG3, DMA Channel 5 and DMA Channel 6.



Bridge mode and HFINTOSC as the selected clock source. Enable CWG3.7. The DMA channels are configured by following these series of steps:

7.1. In the DMAxCON0 register, enable the SIRQEN bit of DMA Channel 1 and clear the EN bit (disable).7.2. Define the DMAxDSZL size to 0x02, which means that the destination is 2 bytes wide.7.3. Configure the DMAxSIRQ to TMR0. Depending on the microstepping resolution, DMAxSSZL will be

0x80 if the mode will be 1/16 microstepping and 0x20 if it will operate in 1/4 microstepping. Thesource and destination addresses are defined in the firmware, depending on the direction of themotor and motor number. Leave the configuration of other registers not mentioned here, as is.

8. In the Pin Manager configuration, set up the input/output pins of all the peripherals as shown in Figure B-1.9. After configuring all the peripherals, click the “Generate Code” button next to the Project Resources tab name

in the top left corner. This will generate a main.c file to the project automatically. It will also initialize themodule and leave an empty while(1) loop for custom code entry.

AN3353Appendix B: MPLAB® Code Configurator (MCC)...


http://ww1.microchip.com/downloads/en/devicedoc/40001725b.pdfhttp://ww1.microchip.com/downloads/en/devicedoc/40001725b.pdf

Figure 9-1. PIC18FXXQ43 Pin Manager Configuration

AN3353Appendix B: MPLAB® Code Configurator (MCC)...


10. Appendix C: Source Code ListingThe latest software version can be downloaded from the Microchip website (www.microchip.com). The user will findthe source code attached to the electronic version of this application note. The latest version is v1.0.

AN3353Appendix C: Source Code Listing


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AN3353


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AN3353


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IntroductionTable of Contents1. Overview2. Stepper Motor Control2.1. Control Overview2.2. Drive Circuit and Control Process2.3. 16-Bit High Resolution PWM for Control Signal2.4. Data Transfer

3. Stepper Motor Control Characteristics3.1. Torque Consideration3.2. Stepping Rate

4. Step Mode Implementation4.1. Full-Step Drive4.2. Half-Step Drive4.3. Microstepping

5. Firmware Flow Diagram6. 3-Axis Control Performance7. Conclusion8. Appendix A: Schematics9. Appendix B: MPLAB® Code Configurator (MCC) Peripheral Initialization10. Appendix C: Source Code ListingThe Microchip WebsiteProduct Change Notification ServiceCustomer SupportMicrochip Devices Code Protection FeatureLegal NoticeTrademarksQuality Management SystemWorldwide Sales and Service

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