Andy Ibbotson wrote: > Thanks Andy. I thought that EMC2 required EPP mode on the parallel port, I > think people are using the board to drive software stepgen. EPP is ONLY needed for Pico Systems and Mesa products that use EPP as a communications path to a controller board. It definitely is NOT required for software step pulse generation and similar things. > I have read the > thread re. the EPP issues and it seems that the fix for the EPP modes is > quite simple? > Going back to the PCI based cards, does the extra speed of the interface > mean that the servo thread can be run faster giving increased update rates > of velocity? I'm trying to assess the benefits of moving from software > stengen to hardware stepgens. > PCI cards definitely are faster than the motherboard parports connected through the ISA-bridge, as they STILL are on a number of motherboards. Some measurements I've made were that a byte transfer on an ISA port ran 800-1000ns, but on a PCI port was in the range of 500-650 ns. I haven't done detailed measurements lately, but on a 600 MHz Pentium III, the entire servo loop for 4 axes, including reading in position, computing the PID and writing out new velocities, took about 60 us with a PCI port, and about 120 us with the ISA. These are very rough numbers from foggy memory.
Given a more modern CPU, I think you could probably run a 10 KHz servo loop without problems, but I'm not sure what sort of machine would actually need such a fast update rate. Maybe if you were contouring at 600 IPM this could be a real concern. All of this is relatively beside the point when you talk about software step generation. My Universal Stepper Controller (USC) can generate step pulse rates over 300,000 per second per axis, with step timing granularity of 100 ns. Compare this to the best software step granularity of maybe 16 us, and you see hardware can do about 160 times better. Also, the USC board can take in encoder signals to close the loop on any step/dir drive, whether the actual motor is a stepper or servo. You can even do this on individual axes, so some can be open-loop steppers, others can be closed-loop. Jon ------------------------------------------------------------------------------ Nokia and AT&T present the 2010 Calling All Innovators-North America contest Create new apps & games for the Nokia N8 for consumers in U.S. and Canada $10 million total in prizes - $4M cash, 500 devices, nearly $6M in marketing Develop with Nokia Qt SDK, Web Runtime, or Java and Publish to Ovi Store http://p.sf.net/sfu/nokia-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
