Hostmot2 Stepper Timing

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18 May 2009 14:57 #295 by BigJohnT
In the sample Hostmot2 configs I noticed that each axis stepgen can be configured for step time, step space, direction setup and direction hold. Some drives step on the rising edge and some step on the falling edge.
In my case I'm using Gecko 203v drives and the timing is:

Step Time 1000us
Step Space 2000us
Direction Hold 200us
Direction Setup 200us
Steps on rising edge

Is the default output for step time the rising edge?

I did some calculations and came up with a max step rate of 333Khz.
Does that sound right?

Should I add any buffer to the timings?

John

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18 May 2009 16:45 #298 by seb_kuzminsky
The hm2 stepgen behaves like the software stepgen in regards to waveform timing. The stepgen waveforms are described in the EMC2 HAL Integrator's Manual (section 13.1 if you're looking at the docs for emc2 2.3).

Whether the machine steps on the rising or falling edge shouldnt matter - it cares about frequency, the timing should be the same in either case.

The maximum step rate is 1/(stepspace+steplen) Hz, so I agree with your computed max step rate.

I would think you wouldnt need to add any buffering to your step timing. The hm2 FPGA should output exactly what you ask for, and your stepper amplifiers should accept what their manual says they accept. Now, that's in theory. If it doesnt seem to work, by all means try giving yourself some margin here. :P

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18 May 2009 17:53 #299 by BigJohnT
Replied by BigJohnT on topic Hostmot2 Stepper Timing
That is good to know that the hm2 stepgen behaves like the software stepgen. I'll add that to the hm2 part of the manual.

In the case of the 203v the step time is 1/2 of the step space so wouldn't that make difference?

If the step time and step space are the same then it won't matter... and the timing is so fast that I just made both of them 2000us.

Thanks Seb

John

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18 May 2009 18:03 #300 by PCW
Replied by PCW on topic Hostmot2 Stepper Timing
HostMot2 stepgen default is active high step output (high during step time low during step space)

Seb: polarity is important because step motor driver inputs are almost always opto-isolated.
Opto isolators often have much slower turn off times than turn-on times, so to reach the maximum step rates
with inexpensive optos, asymmetrical drive timings are used.

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18 May 2009 18:09 #301 by BigJohnT
Replied by BigJohnT on topic Hostmot2 Stepper Timing
Peter,

Thanks for that info.

John

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