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Subject: | Re: question about previous value of ai |
From: | Ralph Lange <[email protected]> |
To: | tech-talk <[email protected]> |
Date: | Wed, 09 Mar 2011 10:47:57 +0100 |
On 09.03.2011 08:55 Silver wrote:
I use an ai record to retrive the value from hardware, in my SNL program, I want to compare the previous value of ai and the new value, then do some action. how can I get the previous of ai?
Either - in the SNL program - by assigning the current value to a local variable as part of your action.Or - in the database - by adding another ai record that pulls the old value from your hardware-ai before processing it via FLNK. (Won't work for I/O scanned hardware ai.)
Or - in the database - by adding a compress record that is configured as a ring buffer, which can hold the arbitrary length history of an ai. Hope this helps, ~Ralph