It doesn't matter what does the counting, fpga, pic, chickens, etc as long as the count is accurate and often enough for the rate of movement. Servo loops using Mesa are 1KHz and faster.
On 7/6/19 12:04 PM, Roland Jollivet wrote: > Hi all > > This might expose my ignorance ;-) and I'm not wanting anyone to do > in-depth calculations for me.. > > In the days of ISA cards, the 8255 was quite popular, but now we're onto > PCI and PCIe > > So, if one looks at the Mesa 5i25, it can read encoders because presumably > because the FPGA is doing the counting. > > Now, if I used one pci-bridge 8255 type card and used all the I/O (A,B,C) > to support 3 encoders, could I use, say a Pic processor to read the encoder > and convert to 8bit data, and then; > These 8bits are presented to the 8255 ports so Lcnc can do a snapshot read > of the encoder values to close a servo loop. > > With 8bit counters on the encoders, would Lcnc read the encoders fast > enough to run a servo based machine comparable to an open loop stepper > system? Obviously it has to read before roll-over or all is lost > > So, lets say the encoder provides 5um linear resolution on an axis, moving > at 10m/min (32ft/min or 0.05Furlong/min ;-) > = 10 000 000um/5um /min > = 2 000 000 counts/min > = 33 333Hz counter rate > > With a /256 pic counter, roll-over will be at 130Hz or every 7.7ms > Could Lcnc cope with that? > > Roland > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
