RE: [CAD_CAM_EDM_DRO] The 250 byte packet viz. ESTOP

Hi Mark,

If the USB dongle is receiving 250 bytes every 10mS and checks the ESTOP and
limit switches every 40uS then even if there wasn't a immediate message to
the PC via USB to tell it that an ESTOP occurred worst case would still be
only 10mS.

But if I was writing the interrupt code and testing limits, home and ESTOP
every 40uS, I'd probably immediately bring down whatever enable line to stop
motion. Plus, since I'm sending out the actual stepping pulses making the
motors move, I could also abort sending out stepping pulses. So, in fact,
response is quick.

In reality, unless you can guarantee that your ESTOP or Limit switches have
no bounce, you'd probably want to wait longer than 10mS anyway. Or perhaps
not.

In either case, an ESTOP or LIMIT or HOME is an EVENT which is reported to
the host on the USB message along with the packet # and the byte # of that
packet so the host will know to the nearest 40uS step pulse when the HOME or
LIMIT or ESTOP happened.

If each 40uS step is on a 5 TPI leadscrew with a 1600 micro-step per turn
leadscrew, then the motor (if it could stop instantly) would at most travel
0.000125"

John Dammeyer

> Or some other event needing instant response - isn't latency
> gonna eat your oysters, or am I missing something? / mark
>