Pulses per rev is exactly the same as steps per rev. Al LinuxCNC cares about is how many step pulses it needs to make to move the machine one distance or angle unit. Typically inches or mm or degrees, but you could use any units. The motor steps per rev is fixed but the drive can "microstep" between these real steps by sending intermediate current levels to the coils. More microsteps will normally be smoother and will give higher resolution, but eventually you will hit the limit of how many steps per second the software can produce. It rarely makes sense to go above 4x microstepping.
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First are full scale Motion Controllers, which we will cover in detail in a moment. The reason is that they are not high enough performance to maintain the exact timing relationships needed to produce a clean pulse train to control multiple servos or steppers.
It takes some very clever coding indeed for software like Mach3 to work on a parallel port, and each new release of Windows seems to make it a little harder. This board is capable of adding 8 inputs, 8 outputs, as well as 3 analog inputs, so it is quite powerful. There are USB boards the Smoothstepper is one that can actually generate step and direction pulses suitable for CNC, but these are more properly motion controllers than breakout boards. See the section below for more.
There are a number of keyboard emulators out there, but I believe the most popular are Pokeys and the iPac, which is sold Ultimarc. The basic iPac provides an additional 28 inputs, which is substantial. There is an enhanced version that allows 56 inputs. For example, I would tend to avoid using them with joysticks. But they are a good way to pick up all the extra buttons on your control panel.
They are so high their makers probably object to comparing them to breakout boards. I only do so because they replace the breakout board. Mach3 works with several, including the Smoothstepper probably the most popular as I write this , the Galil, and others.
These boards offer a tremendous performance upgrade over parallel boards and the like. I have a Smoothstepper, which has worked great. You may also want to read about how to set up a Smoothstepper for my servo-based mill. This is especially true for the higher powered servos on a larger machine. There are boards out there that will do this conversion. What about spindle speed control?
Mach 3, on the other hand, puts out digital pulses, so you need a board to convert from the digital world of Mach 3 on one output pin to the analog realm expected by the VFD. Hopefully the board will isolate the sensitive digital electronics from any potential for line voltages to get back into the digital side as well.
Homann Designs comes to the rescue once again with a couple of boards to perform this function. CNC4PC and others also make boards to do this.
Adapter with DB25 connector
Adapter with DB25 connector