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Table of Contents

List of figures

1 Stepconf Wizard

EMC2 is capable of controlling a wide range of machinery using many different hardware interfaces. Stepconf is a program which generates EMC configuration files for a specific class of CNC machine: those connected to the PC using a standard parallel port and controlled with step & direction signals. Stepconf is installed when you install EMC2 and is in the CNC menu.

Stepconf places a file in the emc2/config directory to store the choices for each configuration you create. When you change something you need to pick the file that matches your configuration name. The file extension is .stepconf.

1.1 Step by Step Instructions

1.1.1 Basic Information

Figure: Basic Information Page

Machine Name
Choose a name for your machine. Use only uppercase letters, lowercase letters, digits, “-” and “_”.
Axis Configuration
Choose XYZ (Mill), XYZA (4-axis mill) or XZ (Lathe).
Machine Units
Choose Inch or mm. All subsequent questions (such as machine travel, leadscrew pitch, etc) will be answered in the chosen units
Driver Type
If you have one of the stepper drivers listed in the pull down box, choose it. Otherwise, find the 4 timing values in your driver's data sheet and enter them. If the data sheet gives a value in microseconds, multiply by 1000. For example, enter 4.5us as 4500. The Gecko type is for the 201 drive. A list is on the wiki site of most popular drives with the timing values is in the Stepper Drive Timing Page.

Additional signal conditioning or isolation such as optocouplers and RC filters on break out boards can impose timing constraints of their own, in addition to those of the driver. You may find it necessary to add some time to the drive requirements to allow for this.

Latency Test Result
Enter the result of the Latency Test here. To run a latency test see section ([.])
Max Step Rate
Stepconf automatically calculates the Max Step Rate based on the driver characteristics entered and the latency test results.
Min Base Period
Stepconf automatically determines the Min Base Period based on the driver characteristics entered and latency test result.
Onscreen Prompt For Tool Change
If this box is checked, EMC will pause and prompt you to change the tool when M6 is encountered. Leave this box checked unless you plan to add support for an automatic tool changer in a custom hal file

1.1.2 Parallel Port Setup

Figure: Parallel Port Setup Page

For each pin, choose the signal which matches your parallel port pin out. Turn on the “invert” check box if the signal is inverted (0V for true/active, 5V for false/inactive).

Output pinout presets
Automatically set pins 2 through 9 according to the Sherline standard (Direction on pins 2, 4, 6, 8) or the Xylotex standard (Direction on pins 3, 5, 7, 9).
Inputs and Outputs
If the input or output is not used set the option to “Unused”.
Include custom HAL configuration
Allows you to add additional hal customizations in the file custom.hal after running Stepconf.

Include custom PyVCP Panel If selected, the PyVCP control panel panel.xml will be displayed on the right-hand side of the main AXIS window. This will not create a PyVCP panel but will create the blank file in the config folder. To create a PyVCP panel see the PyVCP section of the Integrators Manual.

Charge Pump If your driver board requires a charge pump signal simply select Charge Pump from the drop down list for the output pin you wish to connect to your charge pump input. The charge pump output is connected to the base thread by Stepconf. The charge pump output will be about 1/2 of the maximum step rate shown on the Basic Machine Configuration page.

1.1.3 Axis Configuration

Figure: Axis Configuration Page

Motor Steps Per Revolution
The number of full steps per motor revolution. If you know how many degrees the motor is (e.g., 1.2 degree), then divide 360 by the degrees to find the number of steps per motor revolution.
Driver Microstepping
The amount of microstepping performed by the driver. Enter “2” for half-stepping.
Pulley Ratio
If your machine has pulleys between the motor and leadscrew, enter the ratio here. If not, enter “1:1”.
Leadscrew Pitch
Enter the pitch of the leadscrew here. If you chose “Inch” units, enter the number of threads per inch here (e.g., enter 8 for 8TPI). If you chose “mm” units, enter the number of millimeters per thread here (e.g., enter 2 for 2mm/rev). If the machine travels in the wrong direction, enter a negative number here instead of a positive number.
Maximum Velocity
Enter the maximum velocity for the axis in units per second.
Maximum Acceleration
The correct values for these items can only be determined through experimentation. See “Finding Velocity and Acceleration” below.
Home Location
The position the machine moves to after completing the homing procedure for this axis. For machines without home switches, this is the location the operator manually moves the machine to before pressing the Home button.
Table Travel
The range of travel that gcode programs must not exceed. The home location must be inside the Table Travel. In particular, having Home Location exactly equal to one of the Table Travel values is incorrect configuration
Home Switch Location
The location at which the home switch trips or releases during the homing process. This item and the two below only appear when Home Switches were chosen in the Parallel Port Pinout.
Home Search Velocity
The velocity to use when moving towards the switch. If the switch is near the end of travel, this velocity must be chosen so that the axis can decelerate to a stop before hitting the end of travel. If the switch is only closed for a short range of travel (instead of being closed from its trip point to one end of travel), this velocity must be chosen so that the axis can decelerate to a stop before the switch opens again, and homing must always be started from the same side of the switch.
If the machine moves the wrong direction at the beginning of the homing procedure, negate the value of Home Search Velocity.
Home Latch Direction
Choose “Same” to have homing back off the switch, then approach it again at a very low speed. The second time the switch closes, the home position is set.
Choose “Opposite” to have homing slowly back off the switch. When the switch opens, the home position is set.
Time to accelerate to max speed
Distance to accelerate to max speed
Pulse rate at max speed
Information computed based on the values entered above. The greatest Pulse rate at max speed determines the BASE_PERIOD, and values above 20000Hz may lead to slow response time or even lockups (the fastest usable pulse rate varies from computer to computer)
Test this axis
This will open a window to allow testing for each axis. See section ([.])

1.1.4 Spindle Configuration

Figure: Spindle Configuration Page

These options only appear when “Spindle PWM”, “Spindle A” or “Spindle PPR” are chosen in the Parallel port pinout. Spindle Speed Control

If “Spindle PWM” appears on the pinout, the following information should be entered:

PWM Rate
The “carrier frequency” of the PWM signal to the spindle. Enter “0” for PDM mode, which is useful for generating an analog control voltage. Refer to the documentation for your spindle controller for the appropriate value.
Speed 1 and 2, PWM 1 and 2
The generated configuration file uses a simple linear relationship to determine the PWM value for a given RPM value. If the values are not known, they can be determined. For more information see section ([.]) Spindle-synchronized motion (lathe threading)

When the appropriate signals from a spindle encoder are connected to the parallel port, EMC supports lathe threading. These signals are:

Spindle PPR
Also called “Index pulse”, this is a pulse that occurs once per revolution of the spindle.
Spindle A
This is a pulse that occurs in multiple equally-spaced locations as the spindle turns.
Spindle B
(optional) This is a second pulse that occurs, but with an offset from Spindle A. The advantages to using both A and B are increased noise immunity and increased resolution.

If “Spindle A” and “Spindle PPR” appear on the pinout, the following information should be entered:

Cycles per revolution
The number of cycles of the Spindle A signal during one revolution of the spindle

1.1.5 Machine Configuration Complete

Click “Apply” to write the configuration files. Later, you can re-run this program and tweak the settings you entered before.

1.2 Testing Each Axis

Figure: Axis Test Window

With Stepconf it is easy to try different values for acceleration and velocity. First, enter the correct figures for Steps per Revolution, Microstepping, Pulley, and Leadscrew. Then enter a provisional value for Velocity. Next, click Test this axis.

1.2.1 Finding Maximum Velocity

Begin with a low Acceleration (e.g., 2 in/s^2 or 50mm/s^2) and the velocity you hope to attain. Using the buttons provided, jog the axis to near the center of travel. Take care because with a low acceleration value, it can take a surprising distance for the axis to decelerate to a stop.

After gauging the amount of travel available, enter a safe distance in Test Area, keeping in mind that after a stall the motor may next start to move in an unexpected direction. Then click Run. The machine will begin to move back and forth along this axis. In this test, it is important that the combination of Acceleration and Test Area allow the machine to reach the selected Velocity and “cruise” for at least a short distance--the more distance, the better this test is. The formula d=.5*v*v/a gives the minimum distance required reach the specified velocity with the given acceleration. If it is convenient and safe to do so, push the table against the direction of motion to simulate cutting forces. If the machine stalls, reduce the speed and start the test again.

If the machine did not obviously stall, click the “Run” button off. The axis now returns to the position where it started. If the position is incorrect, then the axis stalled or lost steps during the test. Reduce Velocity and start the test again.

If the machine doesn't move, stalls, or loses steps no matter how low you turn Velocity, verify the following:

Once you have found a speed at which the axis does not stall or lose steps during this testing procedure, reduce it by 10% and use that as the axis Maximum Velocity.

1.2.2 Finding Maximum Acceleration

With the Maximum Velocity you found in the previous step, enter the acceleration value to test. procedure as above, adjusting the Acceleration value up or down as necessary. In this test, it is important that the combination of Acceleration and Test Area allow the machine to reach the selected Velocity. Once you have found a value at which the axis does not stall or lose steps during this testing procedure, reduce it by 10% and use that as the axis Maximum Acceleration.

1.3 Determining Spindle Calibration

Enter the following values in the Spindle Configuration page:

Speed 1: 0 PWM 1: 0
Speed 2: 1000 PWM 1: 1

Finish the remaining steps of the configuration process, then launch EMC with your configuration. Turn the machine on and select the MDI tab. Start the spindle turning by entering: M3 S100. Change the spindle speed by entering a different S-number: S800. Valid numbers range from 1 to 1000.

For two different S-numbers, measure the actual spindle speed in RPM. Record the S-numbers and actual spindle speeds. Run Stepconf again. For “Speed” enter the measured speed, and for “PWM” enter the S-number divided by 1000.

Because most spindle drivers are somewhat nonlinear in their response curves, it is best to:

For instance, if your spindle will go from 0RPM to 8000RPM, but you generally use speeds from 400RPM to 4000RPM, then find the PWM values that give 1600RPM and 2800RPM.

1.4 Axis Travel, Home Location, and Home Switch Location

For each axis, there is a limited range of travel. The physical end of travel is called the hard stop.

Before the hard stop there is a limit switch. If the limit switch is encountered during normal operation, EMC shuts down the motor amplifier. The distance between the hard stop and limit switch must be long enough to allow an unpowered motor to coast to a stop.

Before the limit switch there is a soft limit. This is a limit enforced in software after homing. If a MDI command, or gcode program would pass the soft limit, it is not executed. If a jog would pass the soft limit, it is terminated at the soft limit.

The home switch can be placed anywhere within the travel (between hard stops). As long as external hardware does not deactivate the motor amplifiers with the limit switch is reached, one of the limit switches can be used as a home switch.

The zero position is the location on the axis that is 0 in the machine coordinate system. Usually the zero position will be within the soft limits. On lathes, constant surface speed mode requires that machine X=0 correspond to the center of spindle rotation when no tool offset is in effect.

The home position is the location within travel that the axis will be moved to at the end of the homing sequence. This value must be within the soft limits. In particular, the home position should never be exactly equal to a soft limit.

1.4.1 Operating without Limit Switches

A machine can be operated without limit switches. In this case, only the soft limits stop the machine from reaching the hard stop. Soft limits only operate after the machine has been homed. Since there is no switch, the machine must be moved by eye to the home position before pressing the “Home” or “Home All” button.

1.4.2 Operating without Home Switches

A machine can be operated without home switches. If the machine has limit switches, but no home switches, it is best to use a limit switch as the home switch (e.g., choose Minimum Limit + Home X in the pinout). If the machine has no limit switches, or the limit switches cannot be used as home switches for another reason, then the machine must be homed “by eye”. Homing by eye is not as repeatable as homing to switches, but it still allows the soft limits to be useful.

1.5 Latency Test

Generating step pulses in software has one very big advantage - it's free. Just about every PC has a parallel port that is capable of outputting step pulses that are generated by the software. However, software step pulses also have some disadvantages:

Latency is how long it takes the PC to stop what it is doing and respond to an external request. In our case, the request is the periodic "heartbeat" that serves as a timing reference for the step pulses. The lower the latency, the faster you can run the heartbeat, and the faster and smoother the step pulses will be.

Latency is far more important than CPU speed. A lowly Pentium II that responds to interrupts within 10 microseconds each and every time can give better results than the latest and fastest P4 Hyperthreading beast.

The CPU isn't the only factor in determining latency. Motherboards, video cards, USB ports, and a number of other things can hurt the latency. The best way to find out what you are dealing with is to run the HAL latency test.

To run the test, from Applications/Accessories/Terminal (Ubuntu) open a shell and run the following command:


You should see something like this:

While the test is running, you should "abuse" the computer. Move windows around on the screen. Surf the web. Copy some large files around on the disk. Play some music. Run an OpenGL program such as glxgears. The idea is to put the PC through its paces while the latency test checks to see what the worst case numbers are.

Do not run EMC2 or Stepconf while the latency test is running.

The important numbers are the “max jitter”. In the example above, that is 17894 nanoseconds, or 17.9 microseconds. Record this number, and enter it in Stepconf when it is requested.

In the example above, latency-test only ran for a few seconds. You should run the test for at least several minutes; sometimes the worst case latency doesn't happen very often, or only happens when you do some particular action. For instance, one Intel motherboard worked pretty well most of the time, but every 64 seconds it had a very bad 300uS latency. Fortunately that was fixable.

For the latest information on fixing SMI issues goto:

"Fixing SMI Issues"

So, what do the results mean? If your Max Jitter number is less than about 15-20 microseconds (15000-20000 nanoseconds), the computer should give very nice results with software stepping. If the max latency is more like 30-50 microseconds, you can still get good results, but your maximum step rate might be a little disappointing, especially if you use microstepping or have very fine pitch leadscrews. If the numbers are 100uS or more (100,000 nanoseconds), then the PC is not a good candidate for software stepping. Numbers over 1 millisecond (1,000,000 nanoseconds) mean the PC is not a good candidate for EMC, regardless of whether you use software stepping or not.

Note that if you get high numbers, there may be ways to improve them. Another PC had very bad latency (several milliseconds) when using the onboard video. But a $5 used Matrox video card solved the problem - EMC does not require bleeding edge hardware.

1.6 Home and Limit Switch wiring options

The ideal wiring for external switches would be one input per switch. However, the PC parallel port only offers a total of 5 inputs, while there are as many as 9 switches on a 3-axis machine. Instead, multiple switches are wired together in various ways so that a smaller number of inputs are required.

The figures below show the general idea of wiring multiple switches to a single input pin. In each case, when one switch is actuated, the value seen on INPUT goes from logic HIGH to LOW. However, EMC expects a TRUE value when a switch is closed, so the corresponding “Invert” box must be checked on the pinout configuration page.

Figure: Wiring Normally Closed switches in series (simplified diagram)

Figure: Wiring Normally Open switches in parallel (simplified diagram)

The following combinations of switches are permitted in Stepconf:

The last two combinations are also appropriate when a “home to limit” is used.