     The 182 has two words of digital output.  Every property of a
data base device can access one word, or some fraction out of that word.

     The way to set up a 'fractional word' device (or property) is to
bake a mask into the SSDN, which defines which bits belong to this
property.  Thus it is theoretically possible to define the Setting
property for some device as addressing the high byte of one 182 word,
and the Basic Control as addressing the low byte.  For the Setting you
define a mask of FF00, for the status you define a mask of 00FF. 

     The SSDN is thus:

 	Word 0:   mask  mask defining which bits belong to this
			device/property.
	Word 1:	  0020	OID
	Word 2:   ccnn	crate and slot
	Word 3:   20fa  a =subaddress (0 or 1)
			f = 0 (modes 1&2), f = 1 (modes 3&4)

     This SSDN can be defined for both Setting and Basic Control
properties.  Reading-the-setting will return the current state of the
182's bits for this device.

     When you actually transmit a new word to the 182 we support two
modes of operation: simple settings and pulsed settings.  You can run
both the setting and basic control properties either D.C or pulsed.
Furthermore this choice is made by the data you send.  It is not baked
into the SSDN.

     For simple (static) operation send down a single word with the new 
setting.  The mask in the ssdn will be written to the card, followed  
by the new setting.  Only those bits in the setting which are   allowed
by the mask will get changed. 

     If you send two words, and the second word is zero, then the same  
static operation applies. 

     To invoke pulsed operation send two words: the pulsed value and  
the 'pulse mask'.  The pulse mask and the ssdn mask are combined  
(anded) to form a (possibly smaller) mask.  The pulsed value is  
written out under this new mask.  One second later we complement and
write.  The net effect is a 1-second pulse on the selected bits. 

     An example may be in order.  Suppose we want to define Basic Control
to be the 2 high order bits on the high order 182 word:

	bit 2**15=on/off (static)
	bit 2**14=reset  (pulsed)

     We then set up our Basic Control in the data base:

	ssdn =	20FF
		nncc   crate and slot
		0001   subaddress 1 (high order word)
		C000   upper 2 bits belong to this device

	max length is 2 words (so we can pulse)

	pdb =	length is 2 words
		ON mask =	8000 (low word - turn bit 2**15 on)
			 	0000 (high word - no pulsing)
		OFF mask =	0000 (low word - turn bit 2**15 off)
				0000 (high word - no pulsing)
		RESET mask =	4000 (low word - turn bit 2**14 on)
				4000 (high word - pulse bit 2**14 back
					off after 1 second)

     Now suppose we have a 16 bit static Setting for the other 182 chan:

	ssdn =	20FF
		nncc	crate and slot
		0000	subaddress 0 (low order word)
		FFFF	whole word belongs to this device

	max length is 1 word (static operation)

	pdb =	anything that scales to a word full of bits.


     It is also possible to assign a 182 to a Reading or a Basic Status
property, in which case you will read back the current state of the
bits belonging to the device.  This is the same as reading-the-setting.
