							10/10/91 (rev)


	         Front End Support for the 5408 DACs

     The Bi Ra 5408 is an eight channel simple DAC controller. 
Each channel can be strapped as either unipolar or bipolar, and
each can also be strapped for 10.0, 5.0, 2.5 volt full scale
operation.  The card is extremely simple: F(16)A(N) writes a DAC
value, F(0)A(N) reads it back. 

     The front end supports the Setting, Reading, and Basic
Control properties only. 

     Reading is the same as reading-the-setting.  Basic control
is the same as setting: the basic control word received by the
front end is set into the DAC as an analog voltage.  This option
warrants no further description. 

     The SSDNs for all three properties look like this:

          +----------------------------------------------+
          | Dev type=119 (77 hex)|  FF (hex)             |
          +----------------------------------------------+
          | 'N' slot             |  'C' crate number     |
          +----------------------------------------------+
          | Strapping option     | subaddress (0 - 7)    |
          +----------------------------------------------+
          |                 Ramp rate                    |
          +----------------------------------------------+

     Code for strapping option:				
		0 = 10.0 volt bipolar				
		1 =  5.0 volt bipolar				
		2 =  2.5 volt bipolar				
		3 = 10.0 volt unipolar				
		4 =  5.0 volt unipolar				
		5 =  2.5 volt unipolar				

     In Dabbel this looks like:

	SSDNHX SETTNG (77FF/nncc/ddaa/rr)

			cc - Camac crate
			nn - Camac slot
			aa - subaddress  (0-7)
			dd - strapping option code
			rr - ramp rate (may be zero)

     In the database, the setting PDBs for these devices ALWAYS
use primary transform number 2, which is signed 10.0V full
scale.  This is a fairly standard control system view of an A/D
value.  The front end is responsible for the auxilary shifting
necessary to transform between this standard form and the form
needed by the card. 

     Setting data is two bytes long.
					
     Setting values which exceed the full scale limits set by
the strapping on the card are clamped by the front end at full
scale. 

     If the "ramp rate" is zero, then DAC settings happen
immediately upon request.  If the "ramp rate" is non-zero, then
the DAC is slowly ramped up or down from its current value to the
requested value.  The value of the ramp rate is in LSBs per 1/15
sec., so that a value of, for instance, three, will ramp at 45
LSBs per second. 


Extracts of Annotated Sample DABBEL Input
-------- -- --------- ------ ------ -----

EMX (0532/0F0E/0301/0)
       |   |    |
       |   |    +-- DAC Channel 1 (right byte), strapped for +5 V unipolar
       |   +-- Camac slot (left byte) and Camac crate (right byte)
       +-- Magic EMX numbers (=category 5 alarm from front end node 50)

SSDNHX SETTNG (77FF/0F0E/0301/4)
		 |   |    |   |
                 |   |    |   + Ramp to new value at 4 LSBs/sec
                 |   |    +-- DAC Channel (right byte), and strapping (left)
                 |   +-- Camac slot (left byte) and Camac crate (right byte)
                 +-- Special SSDN Camac module identifier (77FF = 5408 DAC)

PRO SETTNG (2, 2, 60, 0)
	    |  |   |  |
	    |  |   |  +-- Force the database to remember your last set value
            |  |   +-- 1 second default display update rate
            |  +-- Maximum size of datum = 2 bytes
            +-- Default size of datum = 2 bytes

PDB SETTNG ('DacV',  'kV',  2,  6, 2, 0, 0, 0, 1.0, 1.0)
              |       |     |   |  |            |    |
              |       |     |   |  |            |    +-- C2
              |       |     |   |  |            +-- C1
              |       |     |   |  +-- Size of datum to convert = 2 bytes
              |       |     |   +-- Common transform: f(x) = C1*x / C2
              |       |     +-- Primary transform: 10.0 V signed full scale
              |       +-- Physical (engineering) units (after both transforms)
              +-- Primary units=D/A V (after only primary transform has applied)

SSDNHX READNG(77FF/0F0E/0301/0)	! Like setting, ramp rate ignored
PRO READNG (2, 2, 60)		! Like setting, no setting value
PDB READNG ('DacV',  'kV',  2,  6, 2, 0, 0, 0, 1.0, 1.0)
