BUCKLE(OPCSDEFS)	  Optical Printer Control System         BUCKLE(OPCSDEFS)

    NAME
        buckle - configure the buckle input ports and bit masks

    USAGE
        buckle [port] [mask] [test] [0]    # (all values in hex!)

    EXAMPLES
        buckle c 0000 00 00	 # No buckle detection for camera chan
        buckle c 03bd 40 40	 # LPT1 pin 10, HI bit detects condition
        buckle c 03bd 40 00	 # LPT1 pin 10, LO bit detects condition

    DESCRIPTION
        If your system has a buckle sensor switches on the camera or projectors,
        they can be wired to one of the IBM parallel ports to allow the software
	to sense its state.

	A buckle sensor temporarily stops shooting to prevent film jams, should
	the film deviate from its normal path and "buckle" into the sensors.

	Buckle conditions are checked whenever a shooting command is executed
	such as KEY, CAM, REP and SEEK. Buckle conditions are NOT tested when 
	linear movement commands such as with GO(OPCS), JOG(OPCS).

        All parameter values are in hexadecimal.

	    [port] is the port number in the range 0000-03ff.
	    If [port] is 0000, no buckle checking is done for that channel.

	    [mask] is applied to the value received from the port 
	    whenever the software is checking for a viewer open condition.
	    This is applied before comparing to [test].

	    [test] is compared to the value read from the port after
	    [mask] is applied. If the result is the same as [test], a viewer
	    open condition exists.

    WIRING CONSIDERATIONS
        Normally you would use an optically isolated interface card for the
        buckle and viewer switches, e.g. PIO-100(DOCS).

        If directly connecting switches to the parallel port, use a separate
        dedicated 5 VDC power supply wired through the switches such that
        when the sensing switch is tripped, +5V is supplied to the computer.

        Such a supply can be a store-bought 5 VDC regulated switching 
        transformer, which gives out *exactly* 5VDC. (Avoid older linear
        transformers, as they are often unregulated)

        As with any signal going to the sensing input on a computer, the
        signal should never be open. The signal must pull either 5 volts 
        or ground for a TRUE or FALSE condition. Open inputs can act like
        radio antennas that will oscillate randomly.

        If you have noise problems, shielded wire can help mitigate noise.
        Shield ONLY at the power supply end. Ground the shield to chassis
        ground if possible.  Keep wire lengths as short as possible.

        If noise problems persist, it may be that the wire is simply too
        long for such a low voltage signal. The PIO-100 uses 12VDC to allow
        for longer cable lengths, and an optoisolator to convert to +5V for
        the parallel port input.

	If noise problems persist, and you have ruled out the computer,
	it may be that the wire is simply too long for such a low voltage
	signal. You may want to use a higher voltage (12 volts) in the
	switch circuitry to drive an optoisolator close to the computer, 
	using the optoisolator to switch a 5 volt current to the port. 

        You can find the base port value for the parallel ports from the
        operating system using the DOS 'debug' utility:

        C>debug                               # run 'debug'
        -d40:8 f                              # enter this (not the '-')
        0040:0008  BC 03 78 03 00 00 00 00    # debug spits this out
        -q         ----- -----                # type 'q' to quit debug
                     |     |
                     |     LPT #2's  port base address
                     |
                     LPT #1's  port base address

        Your machine may show different values. In the case above, 03BC
        is the base port value for LPT1..note the bytes are in reverse
        order in typical LSB/MSB fashion.

        See the PARALLEL() man page which shows the pin out and port addresses
        of the IBM PC's parallel ports.

    BUGS
    	None.

    SEE ALSO
        DEENERGIZE(OPCSDEFS)  - define port/bit to deenergize motors
        ALLSTOP(OPDSDEFS)     - define port/bit to detect the allstop key
        BUCKLE(OPCSDEFS)      - define port/bit to detect film buckles
        VIEWER(OPCSDEFS)      - define port/bit to detect viewer open
        TRIPSWITCH(OPCSDEFS)  - define port/bit to detect trip switches
        SETBIT(OPCSDEFS)      - set bit(s) on a port
        CLRBIT(OPCSDEFS)      - clear bit(s) on a port
        XORBIT(OPCSDEFS)      - invert bit(s) on a port
    	PARALLEL(DOCS)        - parallel port pinout with port/bit masks
        PIO-100(DOCS)         - OPCS Parallel I/O interface board, e.g.
                                http://seriss.com/opcs/pio-100/

    ORIGIN
	Version K1.12e+ Gregory Ercolano, Venice California 04/11/98