On Fri, 27 Feb 2015, Brent Loschen wrote: > Date: Fri, 27 Feb 2015 15:24:48 -0700 > From: Brent Loschen <[email protected]> > Reply-To: "Enhanced Machine Controller (EMC)" > <[email protected]> > To: [email protected] > Subject: Re: [Emc-users] Introduction and a couple questions > > > On 2/21/2015 6:27 PM, Kirk Wallace wrote: >> On 02/21/2015 03:42 PM, Brent Loschen wrote: >>> Greetings everyone! New guy here. I've been following the group for >>> several weeks and feel it's time for an intro and to get some >>> suggestions for a small project I'm working on. >> Welcome to the world of LinuxCNC. >> > Thank you Andy P., Mark W., and Peter W. for your responses to my > original post - most helpful!. My apologies for this delayed response. > > I've been reading everything I can, and I'm weighing the various options > for the desktop mill (to practice on with steppers) vs the Bridgeport > (brushed DC servo ) conversion down the road. I'm not sure if some of > the components used in CNC systems really do have multiple names for the > same functionality, or if there are subtle differences between them. > For instance is a motion controller the same as a PLC or FPGA? In > certain contexts, I get the impression that they are the same, yet in > others, a "motion controller" seems to be a programmable device used > for fixed functionality i.e. robotic pick and place. In my world, PLC's > and FPGA's are discrete semiconductor components, not complete boards > controlled by them!
A PLC or FPGA _can_ both be motion controllers (they are both programable logic devices though a PLC to me is a control appliance in a box where a FPGA is a chip) > > Another question I can't seem to answer is, what's the fundamental > difference between using a standard "bit banged" pport vs using > something like 7i43 or a bus connected 5i25? In the default case (no > special hardware), my understanding is that LCNC toggles the lines of > the pport (step/direction signals?) which are connected to a stepper > drive. What I've not been able to answer, is how the fundamentals > change when using, say a 7i43, connected to the same port? Instead of > sending pulses out the pport, LCNC must instead be sending some kind of > higher level data stream (possibly lower bandwidth? ) to the 7i43 where > it gets converted to precisely timed step/dir pulses - is that right? > If so, what is that data and how is it different from step/dir signals > in the default case? Can anyone comment on the differences or point me > to documentation that explains it? Because high speed operations like encoder counting and step generation may be required at rates that are difficult for a general purpuse CPU (like PC) to do, off-loading these operations to external logic allows improved performance. For step generation, LinuxCNC specifies the step rate and the external hardware generate pulses at this rate until updated by linuxcnc (updates occur at the servo thread rate typically 1 KHz) > > Along the same lines, I've wondered how acceleration/deceleration is > handled. Is it always manged by LCNC regardless of bit banging or > additional hardware, or do FPGA/PLC based boards ever handle that too? As far as I know acceleration is always handled enirely by LinuxCNC Though if you had either a slow servo thread or needed extreme acceleration, it could easily be added to the step generation logic > > Thanks, > Brent > > ------------------------------------------------------------------------------ > Dive into the World of Parallel Programming The Go Parallel Website, sponsored > by Intel and developed in partnership with Slashdot Media, is your hub for all > things parallel software development, from weekly thought leadership blogs to > news, videos, case studies, tutorials and more. Take a look and join the > conversation now. http://goparallel.sourceforge.net/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
