> Note that those setup and hold times are relative to the riseing edge of the (step?) pulse, and the next line is not so specific, but I expect it needs to be checked by a dual trace scope for both > conditions
I'm very tempted to pull the G540 from the router and rig up a test bench test to see if I can get my head around why this is happening. Might get time over christmas. Would be nice to know why inverting the step output works for me, rather than 'it just does' I'm starting to suspect that the 5i25 obeys the set timings, whereas mach on a parallel port uses them as a minimum guide, and frequently exceeds them. > > I have no additional opto-isolation in that path - I believe that the > > G540 uses fast opto's on all the parallel port pins (from the manual, > > I'm sure there was a post on cnczone detailed the choice of isolater > > somewhere) > Thanks for that , so it would have been DIRSETUP/DIRHOLD that I was concerned with. I managed to dig out the thread where Mariss of Gecko was talking about opto circuits. http://www.cnczone.com/forums/general-cnc-machine-related-electronics/23216- optoisolator-circuit.html Posts #2 and #6 are particularly interesting (not sure on cross-post etiquette here), and possibly give a hint as to the root cause of my problem. > > <snip> > And that gives you far finer tools to tune with than software stepping ever will. There may better interfaces than the 5i25, but for us stepper people, its the cats meow. Not bulletproof on its inputs, I didn't have a good enough > grounding setup wrapped around my G0704, and apparently blew the input I was using for a probe. > I don't know as Peter could tell me which chip to replace to rescue it. I AM a C.E.T. and in my dayjob before I retired in 2002/6/30, I could have done it easily, but at 81, my hands aren't as steady as they once were. They do pretty nicely on servo stuff too - I have a 5i25 on the (servo) bridgeport, the (stepepr) lathe was converted earlier, and that has a 5i20 on. > I can't comment based on experience with them so I won't, Ben. Other than to say that 98% of the opto stuff out there, will need a pulse in excess of 1 microsecond on, and often pushing 2 u-s to turn off. I understand there are > some Gas based optos about, but they'd have a serious effect on a BoB's price. One could turn a $15 BoB into a $100 BoB pretty fast. >From the thread above it looks like Gecko use the HCPL-2531 in at least some of their drives - price of $0.87 per 1k doesn't look too bad for a fast dual channel opto. > However, one must bear in mind that when looking at it with a scope, we are watching the voltage, and in opto stuff, voltage doesn't mean near as much as actually measuring the current. Why? Because when the > driving led in the opto goes out, which it might do at 1.85 volts or > as high as 2.4 volts, the load is gone, leaving the voltage to decay toward (which ever rail its headed for) at a very leasurely rate. > Thats a fancy, CMA way to say the scope is lieing to you. So I tend to look at the decay with an eye toward seeing if I can define that point where the down (up?)ward curve changes to a slower rate, then make the "on time" timing > measurements to that point. That can be a difficult point to define even for me, and I've "had a scope probe in one hand" > for 64 years. 64 years ago it was a 5mhz Hickock, today I have 100MHZ dual trace analog, and 200mhz dual trace digitals to go poking around with. > Cheers, Gene Heskett Good to know, I have a rescued tektronix scope which I rarely get to use. Hints on those things that are only learned through experience are always appreciated. I suspect spotting most of the ways phase shift can trip you up even on simple circuits takes quite a bit of practice. Thanks Ben ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
