4 ms·

Timing mostly. These kinds of devices are using the parallel port to "bitbang" everything. Because of that they need rather precise control of timing in order

Timing mostly. These kinds of devices are using the parallel port to "bitbang" everything. Because of that they need rather precise control of timing in order for things to happen when they expect. The USB devices usually just let you send a stream of bytes and they go out without much control over how fast they change. There's apparently some people making usb devices for things like Mach3 and they have some links to them: http://www.cncrouterparts.com/my-computer-doesnt-have-a-parallel-port-can-i-just-get-a-usb-p-154.html http://www.cncrouterparts.com/my-computer-doesnt-have-a-para...

nitrogen 11y ago
Another reason a long time ago was that you could control the built-in port's I/O lines directly by writing to a legacy IO port with a single assembly instruction. Any code written that way would not work with the USB adapters.
toomuchtodo 11y ago
I used a Geckodrive controller to connect via USB to the interface I needed to drive three stepper motors (and speed control for the drill motor) for the CNC mill I built. Works natively with Mach3. The timing is then offloaded to the microcontroller (in this case, the Geckodrive). http://www.geckodrive.com/geckodrive-step-motor-drives/g540.html http://www.geckodrive.com/geckodrive-step-motor-drives/g540....
- nictinkers 11y ago
  That Geckodrive product appears to connect via a standard parallel port. I don't believe Geckodrive has a USB breakout board. You're possibly using the SmoothStepper from Warp9, the KFLOP board from Dynomotion, or one of a couple of Chinese products of widely varying quality. Once upon a time, the upper end of the market used expensive dedicated hardware for CNC motion control. The low end of the market used commodity PCs ruining the signals out the parallel port. Nowadays, the high end of the market is using PCs to do complex motion control (with computer vision etc) and the low end is using variants of Arduino boards with firmware like GRBL. With GRBL, the G-code itself is fed out the USB in a serial stream and the hardware does the motion calculations. Having the motion control in dedicated hardware is much nicer than having it on a PC with an operating system that can interrupt the fast timing loops and as hobby electronics gets more capable, you're going to see this set up more and more.
  - digi_owl 11y ago
    > having it on a PC with an operating system that can interrupt the fast timing loops I wonder if this is also the case for old lab equipment that keep running one some dusty DOS box because replacing the equipment is expensive and time consuming.
StillBored 10y ago
Its more than that, most of the things that utilize the parallel port talked to the IO ports directly for the bit banging. The USB->parallel ones hide the parallel interface behind the windows/etc parallel port driver so that provides an additional roadblock for the old software which otherwise might work.

nitrogen 11y ago

Another reason a long time ago was that you could control the built-in port's I/O lines directly by writing to a legacy IO port with a single assembly instruction. Any code written that way would not work with the USB adapters.

toomuchtodo 11y ago

I used a Geckodrive controller to connect via USB to the interface I needed to drive three stepper motors (and speed control for the drill motor) for the CNC mill I built. Works natively with Mach3. The timing is then offloaded to the microcontroller (in this case, the Geckodrive). http://www.geckodrive.com/geckodrive-step-motor-drives/g540.html http://www.geckodrive.com/geckodrive-step-motor-drives/g540....

nictinkers 11y ago
That Geckodrive product appears to connect via a standard parallel port. I don't believe Geckodrive has a USB breakout board. You're possibly using the SmoothStepper from Warp9, the KFLOP board from Dynomotion, or one of a couple of Chinese products of widely varying quality. Once upon a time, the upper end of the market used expensive dedicated hardware for CNC motion control. The low end of the market used commodity PCs ruining the signals out the parallel port. Nowadays, the high end of the market is using PCs to do complex motion control (with computer vision etc) and the low end is using variants of Arduino boards with firmware like GRBL. With GRBL, the G-code itself is fed out the USB in a serial stream and the hardware does the motion calculations. Having the motion control in dedicated hardware is much nicer than having it on a PC with an operating system that can interrupt the fast timing loops and as hobby electronics gets more capable, you're going to see this set up more and more.
- digi_owl 11y ago
  > having it on a PC with an operating system that can interrupt the fast timing loops I wonder if this is also the case for old lab equipment that keep running one some dusty DOS box because replacing the equipment is expensive and time consuming.

StillBored 10y ago

Its more than that, most of the things that utilize the parallel port talked to the IO ports directly for the bit banging. The USB->parallel ones hide the parallel interface behind the windows/etc parallel port driver so that provides an additional roadblock for the old software which otherwise might work.