Experimental Physics and
Industrial Control System

Ned Arnold <[email protected]> · Wed, 25 Nov 1998 08:12:35 -0600 (CST)

> First off,  Happy Thanksgiving to my American collaborators and their
> families.
> 
> I want to have a record (or record-set) which emulates a set-reset latch.
> My application is to provide a 'processing-active' flag set while a group of
> record processing and sequences are active.
> 
> The BO record does this (latching function) from a medm page using dbPuts to
> the VAL field,  but I want the same effect based on database processing
> links.  That is,  an FLNK from record 'A' should set the latch (VAL =1),
> and an FLNK from record 'B' should reset the latch (VAL=0).
> 
> I feel like I can't see the forest thru the trees on this one.
> 
> 

The simplest method is to use a sequence record, which has a list of up to
10 links to be executed. Use LNK1 to set a BO to 1, use LNK2 thru LNK9 to
process any records you want. Use LNKA to reset the BO. Be careful, the
sequence record does not "wait" for asynchronous records to complete before
executing the next one. Synchronous records are done in order, hoever, even
including FLNKs.

You can implement a set/reset latch with two BO's and a CALC. The BO's 
(one for set, the other for reset) should be set to momentary (.HIGH = .1)
and the CALC can be  ...

	.INPA  -  setBO.VAL CP NMS
	.INPB  -  resetBO.VAL CP NMS
	.INPC  -  calcRecord.VAL NPP NMS
	.CALC  -  A?1:(B?0:C)

	Ned

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System