	  	Front End Support for 279 2-channel
	    Beam Synch Clock Driven Time Delay Generator.


     This is a simple two channel card with delay counters which we
assign to the  Setting (and Reading-the-setting) properties.  We make
the Reading property the same as Reading-the-setting for convenience. 

     The SSDN for all properties is as follows:


		+-------------------------------+
		|		0		|
		+-------------------------------+
		|	0	| OID = 26 (hex)|
		+-------------------------------+
		|  crate	|   slot	|
		+-------------------------------+
		|   26 (hex)	|  channel	|
		+-------------------------------+



Setting, Reading-the-setting, and Reading Properties
-------  ------- --- -------  --- ------- ----------

     It happens that each tick of the clock represents 7 rf buckets of
beam.  It turns out to be convenient to do this factor of 7 scaling
right here, rather than define a new primary transform, so that the user
can see 'primary' units (in rf buckets) and 'engineering' units (in
microseconds). 

     The delay counter on the card is 1 word (16 bits) long.  Since the
scaled values, in terms of rf buckets, are 7 times as large as the delay
count, this scaling forces us to use 2 words for the setting (and
reading) properties. 

     Numerical considerations are:

	1) If, after division, the setting exceeds 16 bits we clamp it
	   at its maximum value.
	2) We also throw away the remainder after division (that is to
	   say, we truncate the result).
	3) All arithmetic is unsigned.


Basic Status Property
----- ------ --------

     The basic status property is a problem all its own. The F(1)A(0)
status readback returns status bits for both timing channels.  We would
like to return a uniform word that is independent of the particular
channel selected.  The mapping from hardware status to the interpreted
status is as follows: 

	F(1)A(0) word:	e1/e0/a1/a0/t1/t0/bs/tc

			  e1,e0 - channel enabled (1 bit for each chan)
			  a1,a0 - channel armed    "  "   "   "    "
			  t1,t0 - channel timing   "  "   "   "    "
			  bs    - beam sync clock present
			  tc    - tclock present

	We return a word: 0/0/0/en/an/tn/bs/tc

			  en,an,tn - either e0,a0,t0 or e1,a1,t1,
				     depending upon channel selected
			  bs & tc  - as above, same for both channels

     The basic status word, and thus the Basic Status PDB, is entirely
independent of channel number on the card.


Basic Control
----- -------

     We also have simple basic control -- off=1 / on=2 for each channel,
reset=3 applies to the whole card.
