Re: [CAD_CAM_EDM_DRO] Hardware step generator idea

> > It seems to me that this card could take the form of an 8254
> > programmable timer (3 channels) running from a suitably fast clock
> > source and something (74hc373, 8255) to provide bits for the direction
> > signal. (Software might also need to control the 8254 gate output when
> > zero speed is commanded)
>
> These 8-bit timers do not have enough timing resolution to work well.
> I am using a 24-bit counter running at 10 MHz, to give resolution of 100
> nS, and a minimum speed of .6 steps/sec (below that, the computer has to
> turn the pulse gen on and off).
>

Actually they are 16 bit. In the original pc the clock to the 8253
was 1.19 mhz, which when divided by 65536 gives the 18.2 hz timer tick.

I do see the potential problem, though. With a 10mhz clock you get
decent timing at 100 khz step rates (roughtly 1khz steps) but the
minimum step rate is 152 Hz. Still, 152 Hz is well below the cycle
time of EMC, so it would be entirely reasonable to switch to discrete
pulses at that range.

OTOH, the 24 bit counters probably aren't that much more expensive and
would make the software simpler.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
22 Adrian Street, Somerville, MA 02143
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