The parallel (printer cable) port is uses the computer as its main source of pulse trains to operate the motor driver directly. Parallel ports are a direct connection from the processor commonly referred to as GPIO pins (General Purpose I/O pins) and provides a convenient and powerful way to interface with the computer. The parallel breakout board is included in those kits only to condition those signals for use with the drivers.
The USB serves at the actual controller, sending the pulse trains, but the computer sends simple human readable instructions to the USB controller to tell the controller how to send pulses.
The non-technical differences that may serve as the most important information to you is that the parallel configurations allow for a wider variety of industry standard software that can be used to control the cnc machine. The USB that we offer requires the operator to use a software called Planet-CNC software which is a very well made and feature full cnc control software.
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WHAT IS THE DIFFERENCE BETWEEN A PRINTER CABLE PORT AND USB MOTOR KITS