Till Harbaum / Lists wrote: > Hi, > > i am slowly preparing to become an active emc user. I'd finally like to build > something USB based as already discussed on the developer list, but before > that i'd rather use some printer port solution to get a working setup. The > PC i am going to use is working and the live cd seems to work reliably after > adding the smi patch. I also have a nice 8" svga tft screen with touchscreen > that works nicely with the live-cd. Actually "touching" the buttons in the > axis gui is very cool ... > > I am now thinking about getting a CNC-enabled Proxxon MF70. This one is > delivered with the emis smc800 card as mentioned in at least two > other threads in this list. Those rather short conversations quickly ended > with "this would be rather complex". > > I am not convinced that it's really that complex. The smc800 uses 2 data > lines of the printer port to select one of its three axes. Doing subsequent > writes to the remaining bits causes the bits being written to be latched in > one of the three axis registers. These latched bits then drive the motors > coils. In order to actually drive a motor, you periodically cycle these bits > through eight patterns making the motor spin. > > This cannot be directly driven by the current stepper driver as i understand. > But making it work should imho be rather simple. Currently the "step" > and "direction" bits are directly forwarded to the printer port. The smc800 > would just require some tiny addintional software layer that takes the > direction and step bits, keeps an internal counter which is being updated > based on the step and direction info. And whenever such a counter changes, it > writes a control pattern for the related axis to the printer port. There is a quadrature output setting for the stepper driver. it currently sends 4 pairs of quadrature outputs on the 8 data lines. It is not clear from your description whether the 3 axes of the smc800 are on separate pins, or all multiplexed through the same pair of pins. If multiplexed, then only 4 pins are actually used. I believe the quadrature output signals would be the same as your "drive the motors coils" for full-step operation. Either way, it shouldn't take a big overhaul to change the behavior of the stepper driver to do this. But, having to multiplex the step signals could substantially slow the available step rate.
Also, you should know that not having microstepping severely limits the performance of a stepper system. If you haven't experienced what a good microstepping drive can do, you really need to see something with a Gecko 201 drive run to appreciate it. I don't like steppers for positioning applications with greatly varying loads and speeds, but if you want to go with steppers, you really want microstepping. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
