XORBIT(OPCSDEFS)	Optical Printer Control System	  XORBIT(OPCSDEFS)

    NAME
        xorbit - invert bit(s) on a port using exclusive-or (XOR)

    USAGE
        xorbit [port] [mask] [softlatch]    # (values hex!)

    EXAMPLES
        xorbit 0378 04 0     # flip lpt1 port bit #2 (1=#0, 2=#1, 4=#2)
        xorbit 0306 01 1     # kuper card logic connector,
	                     # flip bit #1 (note softlatch=1)

    DESCRIPTION
        This command flips bits on a port, based on the mask. 
	All bits specified by the mask are inverted. (set will be clear,
	clear will be set, etc)

	[port] is the port number in hex.

	[mask] is a hex byte value indicating the bits to be flipped
	on that port. 

    CAVEATS
        o With [softlatch] set to 1, only ports 0x0000 - 0x07ff are allowed.
          Any ports above 0x07ff with [softlatch] enabled causes an error.

        o External programs changing port bits defined to OPCS with [softlatch]
          (e.g. the kuper logic I/O port) should be aware that OPCS is
          maintaining its own internal latch for that port, and that latch
          won't know about hardware changes made by external programs.
        
        o Due to these issues, it's best to avoid using hardware that has to
          be latched. It's usually bad hardware practice to make WRITE ONLY
          ports, since different programs cannot co-communicate with them,
          unless some common data area or driver is arranged.

    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

    ORIGIN
	Version K1.12d+ Gregory Ercolano, Venice California 03/04/98