Help with Pololu DRV8711 Stepper Motor Driver

[Atom058]

Hello - I am trying to write a simple program to run a stepper motor back and forth using the Pololu DRV8711 driver (Link: https://www.pololu.com/product/3730). In order to use the driver, you must first enable it and then you can use the DIR and Step Pins to run your stepper. With other drivers, all you needed to do was drive the ENABLE pin high and you were good to go. With the 8711 board, you have to enable it via SPI. This is done by sending 16-bit values to the registers on the board. Page 27 of the data sheet for this (Link: https://www.ti.com/lit/ds/symlink/drv8711.pdf) shows the registers and gives the default values. Technically, all I should have to do is to set bit 0 of the CTRL register to 1 and that should enable the motor, correct? I also want to limit the current to 1/2 of it's maximum value of 4A. This is done using the lower 8 bits of the TORQUE register. Here is my routine to do that:

'****************************************************************
InitStepper1:
    'Set current to 1/2 max (2A) 
    '$1180 = %0001000110000000
    high M1SCS
    Shiftout m1SDAT, M1SCLK, 1, [$1180/16]
    low M1SCS
    
    pause 50
    'Enable Motor
    '$0C11 = %0000110000010001
    high M1SCS
    Shiftout m1SDAT, M1SCLK, 1, [$0C11/16]
    low M1SCS    
    
    return
    
'****************************************************************

I am leaving all of the other values at their default. After executing the InitStepper1 code, I go to stepping the motor by pulsing the STEP pin and nothing happens. My stepper spins freely and I get no indication from my power supply that there is any additional current draw. Is there something I am not doing or doing wrong? Thanks! Jeff

[HenrikOlsson]

Looks like you're shifting out $1180 divided by 16, truncated to 8 bits, so $22. That's not what you want, is it?

Be careful with / vs \ ;-)

[Atom058]

THANKS! Good catch and yes, I feel stupid. I will give this a try and let you know if that was it! Jeff

[Atom058]

Well, While that was a problem, it was not THE problem. Still no movement. I tried both mode 1 and mode 0 for the SHIFTOUT methods, also, to no avail.
Here is a snip of the circuit board design for examination. It seems pretty straight forward, so I think my issue is with setting the registers. Any thoughts are appreciated.
NOTES: There are 2 drivers on board. Green traces = 5V, Blue = Gnd, Red = 12V, Black = Signal. PIC = PIC16F877A. Thanks!

[HenrikOlsson]

Hmm...PortA...have you disabled the analog functions (ADCON1 and CMCON registers, I believe)?
Have you verified (logic analyzer or scope) that the expected data does appears on the pins?

[Atom058]

Yes, I did set ADCON1 and no, I have not used a scope on this yet. Here is the entire code. I am simply trying to initialize the driver and run a stepper back and forth with 2 LEDs that indicate which direction. I really feel that there is some initialization that I am not doing or not doing correctly. Other than setting the torque and enabling the driver, I am using all the other register defaults... Thanks!

'****************************************************************
    DEFINE OSC 20
@ DEVICE HS_OSC
  
    TRISA = %00000000
    TRISB = %10111111
    TRISC = %01110000
    TRISD = %00000000
    TRISE = %00000000

    ADCON1 = 7          ' Set PortA Pins as I/O pins 
    
'   M1 = Stepper1
    M1SCS       var PORTB.6
    M1SCLK      var PORTA.0
    M1SDAT      var PORTA.1
    M1DIR       Var PORTA.2
    M1STEP      var PORTA.3
    
    RedInd      var PORTD.0
    GrnInd      var PORTD.1
    
    Icnt        var word
    M1NumSteps  var word
    M1Delay     var word  'delay between steps - 250-12500 uS

'    CTRL Register
'    EnableON = %0000110000010001   '$0C11
'    EnableOFF = %0000110000010000  '$0C10
    
'    Torque Register
'    Torque50 = %0001000110000000  'Set current at 50% (2A) $1180
'    Torque100 = %0001000111111111  'Set current at 100% (4A) $11FF
    
'****************************************************************
    low RedInd
    low GrnInd
    
    low M1SCS ' Set reset pin low
    low M1Sclk ' Set clock pin low
    low M1Step
    
'****************************************************************
    pause 1000
    
    goto TestStepper1

'****************************************************************
'****************************************************************
TestStepper1:
    gosub InitStepper1
    M1numsteps = 4000
    M1Delay = 5000 'uS between steps

DoAgain1:
    high RedInd
    low GrnInd
    
    low M1DIR 'CW
    for icnt = 1 to M1numsteps
        high M1step
        pauseus 10
        low M1Step
        pauseus M1Delay
    next

    low RedInd
    low GrnInd
    pause 1000 
    low RedInd
    high GrnInd 
     
    high M1DIR 'CCW
    for icnt = 1 to M1numsteps
        high M1step
        pauseus 10
        low M1Step
        pauseus M1Delay
    next
    
    low RedInd
    low GrnInd
    pause 1000
    goto DoAgain1        
        
'****************************************************************
InitStepper1:
    'Set current to 1/2 max (2A)  
    '$1180 = %0001000110000000
    high M1SCS
    Shiftout m1SDAT, M1SCLK, 0, [$1180\16]
    low M1SCS
    
    pause 50
    'Enable Motor
    '$0C11 = %0000110000010001
    high M1SCS
    Shiftout m1SDAT, M1SCLK, 0, [$0C11\16]
    low M1SCS    
    
    return
    
'****************************************************************
    End

[amgen]

looks like it wants MSB first..... mode 1 on shiftout ???

[Atom058]

Amgen - Thanks for your input. Yes, I have tried both Mode 0 and 1 with no luck. I have also tried reversing the SCS pin (low, shiftout, high as opposed to high, shiftout, low) and nothing there either. I still think there is something in one of the registers that I am not setting correctly...

[Atom058]

OK - Problem solved. I went to Pololu and got help from their tech folks and they helped me figure this out. In a nutshell, it had to do with how I was creating the CTRL and TORQUE registers and sending them out. If you want to see how that all played out, just go to this link: https://forum.pololu.com/t/using-a-d...c-pro/27792/13. Don't see any reason to re-hash it here. In any event, I am now able to set the registers and control my stepper nicely. Here is my updated code that should get you started. The Pololu PNs for these boards is 3730 and 3731. Enjoy!

'****************************************************************
'*  Name    : Pololu Stepper-DRV8711.BAS                        *
'*  Author  : Jeff Wheat                                        *
'*  Date    : 05/21/2025                                        *
'*  Version : 1.0                                               *
'*  Notes   : PIC16F876A                                        *
'*          : Uses Pololu 4&8A Driver Boards                    *
'****************************************************************
@ DEVICE HS_OSC
    DEFINE OSC 20

    ADCON1 = 7 ' Set PortA Pins as I/O pins    
       
    TRISA = 0
    TRISB = 0
    TRISC = %00001111
              
    ' Define the LCD Hookup parameters
    ' data pins D4-D7 are hooked to pins B.0-B.3, respectively
    define LCD_DREG     PORTB   'Data Port = PORTB
    define LCD_DBIT     0       'Data starting bit = 0
    define LCD_RSREG    PORTB   'Register Select Port = PORTB
    define LCD_RSBIT    7       'RS bit = PortB.7
    define LCD_EREG     PORTB   'Enable Port = PORTB
    Define LCD_EBIT     4       'Enable Bit = PortB.4
    define LCD_BITS     4       'LCD Bus Size = 4
    define LCD_LINES    2       'Number of lines on LCD
       
    MenuBtn     var     PORTC.0
    UpBtn       var     PORTC.2
    DnBtn       var     PORTC.1
    EnterBtn    var     PORTC.3

    DirPin  	var     PORTA.3
    StepPin 	var     PORTA.5
    SDATO       var     PORTA.1  'connect to SDATI pin on driver board
    SDATI       var     PORTA.2  'connect to SDATO pin on driver board
    SCLK        var     PORTA.0
    SCS         var     PORTC.7
    
    Icnt        var     word
    StepDelay	var	    word
    StepMode    var     byte
    NumSteps    var     word
    DataOut     var     word
    DataIn      var     word
    
    Line1       con     $80
    Line2       con     $C0
    
    LSBFirst    con     0
    MSBFirst    con     1
    
 '****************************************************************    
    low steppin
    low DirPin
    low SCS
    
    pause 500 
    LCDOUT $FE, 1 ' Clear LCD screen 
    pause 20
    
    lcdout $FE, line1, " Pololu Stepper "
    lcdout $FE, line2, " Board - DRV8711"

    pause 2000
    LCDOUT $FE, 1

    gosub InitStepper
    pause 50
    
'    Gosub ReadRegisters
'    Stop
    
    Numsteps = 4000
    StepDelay = 500 'uS between steps
    
'****************************************************************
Start:
    lcdout $FE, line1, "Dir = CW "
    
    low DIRpin 'CW
    for icnt = 1 to numsteps
        high stepPin
        pauseus 10
        low StepPin
        pauseus StepDelay
    next

    pause 1000
    lcdout $FE, line1, "Dir = CCW" 

    high DIRpin 'CCW
    for icnt = 1 to numsteps
        high steppin
        pauseus 10
        low Steppin
        pauseus StepDelay
    next
    
    pause 1000
    goto Start        
        
'****************************************************************
ReadRegisters:
    'Read CTRL register 000
    DataIn = 0
    DataOut = %1000  
    high SCS    
    Shiftout SDATO, SCLK, MSBFirst, [DataOut\4]      
    Shiftin SDATI, SCLK, MSBFirst, [DataIn\12]      
    low SCS  
    
    lcdout $FE, line1, bin DataIn  'Display result in binary
    
    'read TORQUE register 001
    DataIn = 0
    DataOut = %1001  
    high SCS    
    Shiftout SDATO, SCLK, MSBFirst, [DataOut\4]      
    Shiftin SDATI, SCLK, MSBFirst, [DataIn\12]      
    low SCS 
    
    lcdout $FE, line2, bin DataIn
          
    Return    
        
'****************************************************************
'****************************************************************
InitStepper:    
    'TORQUE Register - Set current to 1/2 max (2A for 36v4 and 4A for 36v8)
    '         BIT0              BIT15
    'DataOut = %0 001 0 000 11011111  
    DataOut = %0001000011011111      
    high SCS
    Shiftout SDATO, SCLK, MSBFirst, [DataOut\16]   
    low SCS
    
    'CTRL Register - Enable Motor
    'DataOut = %0 000 11 11 0 0010 0 0 1
    'DataOut = %0000111100000001  'full step
    DataOut = %0000111100001001   '1/2 step
    'DataOut = %0000111100010001  '1/4 step
    high SCS
    Shiftout SDATO, SCLK, MSBFirst, [DataOut\16]       
    low SCS 
          
    return
    
'****************************************************************
    end