Hi,
ISIG_SPINDLE_AT_SPEED is a signal defined within Mach4. Its intention is to be hooked to an output of your VFD.
The signal itself does nothing unless you code it to do so.
For instance you might issue a an M3 (turn the spindle on) and then wait until the input signal ISIG_SPINDLE_AT_SPEED to
become active before executing more Gcode.
Most VFDs have a number of programmable outputs, SPINDLE_AT_SPEED is one.
As per the Manual-The time to accerate the spindle in the slected range.
This is a totally different setting. It is your estimation as to how long the spindle will take to accelerate. If say the VFD
was faulty and despite the spindle being turned on it did not spin up like it should Mach wouldn't know, it would
still start executing Gcode 4 seconds after the turn on signal (4 secs being what you set the accel time in the table).
That's where you could use the ISIG_SPINDLE_AT_SPEED signal because it will ONLY become active if the VFD says so.
Craig