PPR(OPCSDEFS)		Optical Printer Control System		PPR(OPCSDEFS)

    NAME
        ppr - configure the 'pulses per revolution' for a motor

    SYNOPSIS
	ppr [chan] [pulses]

    EXAMPLE
	ppr a 2000            # microstepper system
	ppr a 4000            # microstepper with vistavision
	ppr a 400             # half stepper system

    DESCRIPTION
	Sets the number of pulses needed to rotate a motor one revolution.
	This command exists especially for the CAMERA and PROJECTOR motors.

	Keep in mind the OPCS hardware runs stepper motors at more than the
	motor's rated resolution. Microstepper systems can have as many as
	2000 pulses per rev, and half stepper systems can have 400 per rev.

	The software uses the PPR value in two ways. One is to obviously 
	translate frames into physical steps for the motors. The other
	is for the ALLSTOP logic to know when to check for the ALLSTOP key,
	so as not to stop the shutter mid-revolution.

    NOTES
        PPR settings for the fader are never used by the software, since
	revolutions have no meaning in the context of running the shutter.

	PPR values should be divisible by two, esp. for the projector so that
	half phase shifts calculate to non-fractional steps.

    BUGS
	You cannot specify floating point values for PPR. This is not actually
	a bug: if your hardware is geared in such a way that a full revolution
	occurs in a fractional number of steps, you should probably fire the
	guy who built it and have the hardware rebuilt anyway.

        To avoid a nasty bug with the ALLSTOP key, and to have counters
	update properly, configure the PPR(OPCSDEFS) command for the 
	D thru L channels to be '10' in your OPCSDEFS.OPC file, regardless
	of the actual number of pulses per revolution. This also ensures 
	slewing in JOG doesn't go in very large increments.

	    ppr  d  10	# non-shutter channels only
	    ppr  e  10
	    ppr  f  10
	    ppr  g  10
	    ppr  h  10

    ORIGIN
	Gregory Ercolano, Los Feliz California 11/29/89