Re: [CAD_CAM_EDM_DRO] cant see parallel port from dos

deanc500 wrote:

>Hi, I am having trouble running my cnc control software in dos. I have
>a 1Ghz Toshiba Sat Pro laptop running Win98. I can run kellycam and
>master5 in windows but step rates are too slow. When I exit windows to
>"dos" or win 98's version of it, the software does not see the
>parallel port.
>Anyone seen this before?
>
>

Of course. The environment when running Win 95 and newer (and that
includes the "DOS"
window in Windows), "virtualizes" the parallel port. This means that
your DOS program is
not actually allowed to alter the registers of the parallel port chip,
it is talking to a
program that simulates the response of the chip. This software decides
what functions of
the parallel port you can, and CAN'T access from DOS emulation. Windows
95 let you
do nearly anything except change the mode (SPP, Bi-Dir, EPP, ECP, etc.).
Win 98 is
much more restrictive. There is a program called DirectIO that is
supposed to make
this protection disappear, but I couldn't get it to work before the
trial period expired.

DOS ran in "real" mode, where the CPU had unfettered access to all the
hardware.
Windows, and DOS emulation under the DOS window, the cpu is in protected
mode,
and all hardware is off-limits, other than the chunk of memory made
available to the
program. Any time you attempt to touch a hardware register, an
interrupt to a supervisor
program is made, and it decides whether to allow the access or not.

Jon