					27 July 1983
					22 July 2008 update by G. Johnson


TO:	 Distribution

From:	 M. Glass

Subject: New SSDNs for 175 clock event generators


     Starting today DEC-S 175 type clock event generators will need to be
entered into the data base in a new way.

     The new format involves one device per clock event, i.e. up to 16 devices
per camac card.  The old format involved one device per card; there are three
of them currently in the data base.  The old devices will remain in the data
base until the 48 (3*16) new devices are added and Therese Watts changes her
programs to use the new devices.  At that point the old devices become
obsolete.  No more 175s will be added in the old format. 

     Consult Therese about the details of the 48 new devices.

     The new 175 devices support four properties, to wit: reading, setting,
basic status, and basic control.  All four properties are added to the data
base for each device.  All use an identical SSDN.

     The new SSDN looks like this:


		+---------------------------------------+
		|	00	    |	    00		|
		+---------------------------------------+
		|	00	    |	OID = 0F (hex)	|
		+---------------------------------------+
		| 'C'  crate number |	'N' slot	|
		+---------------------------------------+
		|	00	    | channel # (0-15)	|
		+---------------------------------------+


     The channel number goes from 0 to 15 (decimal) where channel 0 is the one
you get by addressing F(0) A(0) on the card. 

     The reading and setting properties both have default lengths of one word.
You can read or set a single event number, which is in the low order byte of
that word.  There is no scaling for either reading or setting.

     The basic status property is also one word.  Only the low order bit is
meaningful.  It contains 1 if the 175 channel (with the event written into it)
is enabled, 0 if the channel (event) is disabled.  The basic status PDB should
be set up so that this bit turns into ON and OFF.

     For basic control you send one word containing 3 possible values thusly:

		1  -  disable the channel (and thus the event).
		2  -  enable the channel
		3  -  trigger the event

     The basic control PDB should be set up so these values are returned for
OFF, ON, and RESET respectively.

     If you have any questions see either Therese or me.


Distribution
------------

D. Beechy
N. Gelfand
G. Johnson
S. Sommers
T. Watts
