Re: stepper pulse rate idea

[Jon Elson <elson-at-pico-systems.com>]

jmkasunich-at-ra.rockwell.com wrote:

>
>
>Ray's gearshifting idea has prompted me to float one of my own.
>I considered this a while ago but didn't post it or follow up.
>
>If I understand it correctly, the existing stepper routines
>can generate only one step pulse for every two executions of
>the high speed interrupt.  The first sets the output, the
>second clears it.  The maximum step rate could be doubled
>if we could generate a step pulse on every interrupt.
>
>There are at least two ways to reach that goal.  Both would
>require some external hardware, but it probably would be
>less than an pulse multiplier or gearshifter.
>
>1)  Instead of setting the step bit in one pass of the
>code and clearing it in the next, set and clear it in
>the same pass.  This would result in a very short step
>pulse (1uS or less).  Then use an external one-shot to
>stretch the pulse enough to make the drive happy.
>  
>
Or, put an edge detector (XOR gate and an RC delay for one input) and a 
one shot
on the step signal.  Any change, of either polarity, causes a step pulse 
of whatever
length you set the one shot for.

This would require the most trivial change to the software, and would 
require only one
I/O per step.

Jon