Pinout of the grbl-mega

[CognitiveConnexionist]

Hello, thanks for putting out a version of grbl that has backlash correction. I have not been able to test it because I could not find the pinout or connections that go to/from the mega board. Can you please confirm that backlash works for arc corrections without transforming arcs into short lines? Thanks for your answers!

[shooter64738]

The pinout wasnt changed and should be the same as the standard grbl kega version.

Grbl converts arcs into short line segments as its way of interpolation of arcs. This version functions the same way and as each segment is queued, if a segment will cause a direction change in the axis, backlash comp will run.

[shooter64738]

The pin names are in the comments on the right.

define STEP_DDR DDRA

define STEP_PORT PORTA

define STEP_PIN PINA

define X_STEP_BIT 2 // MEGA2560 Digital Pin 24

define Y_STEP_BIT 3 // MEGA2560 Digital Pin 25

define Z_STEP_BIT 4 // MEGA2560 Digital Pin 26

define STEP_MASK ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits

// Define step direction output pins. NOTE: All direction pins must be on the same port.

define DIRECTION_DDR DDRC

define DIRECTION_PORT PORTC

define DIRECTION_PIN PINC

define X_DIRECTION_BIT 7 // MEGA2560 Digital Pin 30

define Y_DIRECTION_BIT 6 // MEGA2560 Digital Pin 31

define Z_DIRECTION_BIT 5 // MEGA2560 Digital Pin 32

define DIRECTION_MASK ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits

// Define stepper driver enable/disable output pin.

define STEPPERS_DISABLE_DDR DDRB

define STEPPERS_DISABLE_PORT PORTB

define STEPPERS_DISABLE_BIT 7 // MEGA2560 Digital Pin 13

define STEPPERS_DISABLE_MASK (1<<STEPPERS_DISABLE_BIT)

// Define homing/hard limit switch input pins and limit interrupt vectors. // NOTE: All limit bit pins must be on the same port

define LIMIT_DDR DDRB

define LIMIT_PORT PORTB

define LIMIT_PIN PINB

define X_LIMIT_BIT 4 // MEGA2560 Digital Pin 10

define Y_LIMIT_BIT 5 // MEGA2560 Digital Pin 11

define Z_LIMIT_BIT 6 // MEGA2560 Digital Pin 12

define LIMIT_INT PCIE0 // Pin change interrupt enable pin

define LIMIT_INT_vect PCINT0_vect

define LIMIT_PCMSK PCMSK0 // Pin change interrupt register

define LIMIT_MASK ((1<<X_LIMIT_BIT)|(1<<Y_LIMIT_BIT)|(1<<Z_LIMIT_BIT)) // All limit bits

[CognitiveConnexionist]

Thank you very much for your answer, just another question, while one axis is getting its backlash corrected, does the other axis stop moving until the backlash has been corrected?

[shooter64738]

Yes. Because of the way motions are queued in grbl, the backlash motion will only move the axes that change direction. The comp should be fast taking only a millisecond ( unless you are comping extreme backlash). The tool should not have a noticeable 'rest' during compensation.

My other controller (Talos) behaves differently on backlash comp, but this was the only practical way to fit it into base grbl.

[skitter155]

Is it possible to use a CNC shield for the uno on the mega with this code? Or are the pins incompatible?

[shooter64738]

As far as I am aware the pin assignments between the Uno and Mega version are incompatible.

[TomMandle]

Hi, I used the GRBLDuino Mega Lite-GRBL 1.1 Arduino CNC Shield from Tindie.  It worked well with my Bridgeport CNC  conversion. The backlash version is fantastic.  Thank you for creating it. A request for fixing a small defect.  When the table comes up to enter the parameters, the x,y,z backlash items are missing the "description" for $140, $141, $142. Thank you again.

[shooter64738]

Hi, I used the GRBLDuino Mega Lite-GRBL 1.1 Arduino CNC Shield from Tindie.  It worked well with my Bridgeport CNC  conversion. The backlash version is fantastic.  Thank you for creating it. A request for fixing a small defect.  When the table comes up to enter the parameters, the x,y,z backlash items are missing the "description" for $140, $141, $142. Thank you again.

If I get some spare time, I'll add descriptions.

I spend most my time working on my other control, and when Ive got a feature in it I can port to grbl, I try to get it in there.