SLOP(OPCS)		Optical Printer Control System		SLOP(OPCS)

    NAME
        slop - configure 'slop correction' for sloppy hardware (eg. faders)

    SYNOPSIS
        slop [chan] [steps]

    EXAMPLES
        slop d 300	# indicates the fader has 300 steps of 'slop'

    DESCRIPTION
        SLOP tells the software to take up slop for a motor whenever it is
	told to run in a prescribed direction.

	The sign of the [steps] arguments tells the software which direction
	it should prefer to take up slop in. A positive number takes up
	slop when the motor moves in a positive direction, a negative number
	takes up slop in the negative direction.

	To determine how much slop a motor has, disable any slop commands for
	the motor. Use JOG(OPCS) to move the motor in one direction. Now 
	change directions, making note of how many steps you can tell the 
	computer to run in the new direction before the equipment starts
	to actually move. Use this number of steps in the SLOP(OPCSDEFS)
	command for that motor, and note how the software tries to take up
	the slop.

	If the motor is being moved by a command in the direction the software
	wants to take up slop, the software will move the motor that many 
	pulses BEYOND the position requested, and then back that many pulses
	to take up slop. This technique ensures the equipment is always
	resting on the same edge of the sloppy equipment, which can allow
	accurate positioning of even the sloppiest mechanics.

    NOTES
	For those of you who think it is a waste to have to take up slop
	EACH TIME the motor turns in the predefined direction, and that
	'it should only take up slop once..when it changes direction',
	think again, pal. You are assuming the slop distance is a fixed
	entity, which it rarely is.
	
	In order to arrive at positions properly, the position must be found
	by always leaving off having moved to the position FROM THE SAME 
	DIRECTION, so that the equipment is always left off resting on the
	same side of the equipment slop. This necessitates always doing the
	double-move slop take up whenever the motor moves in one of the two
	directions.

    BUGS
        none.

    SEE ALSO
        INTERP(OPCSDEFS)
	GO(OPCS)

    ORIGIN
	Gregory Ercolano, Los Feliz California 12/15/89