Experimental Physics and
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First, I think 1.0V is not going to work as TTL low. For at least some logic families, you need to be below 0.6V, and that's with zero noise margin. The safest value for TTL low is 0.0V. I don't see any problem with this idea. I would have the mbbo set the output to 0V or 5V, if the mbbo value is "low" or "high", and not set it at all if the mbbo value is "undefined". I would have the mbbi report "low" for voltages < 0.6V; "high" for voltages > 2.4V; and "undefined" otherwise. I would have the mbbo's value follow the mbbi's value, but arrange that the mbbo will not drive the output when the mbbo is being driven by the mbbi. This is easy to accomplish: have the mbbo write through a second mbbo record which is scan-disabled by the PACT field of the mbbi record. Also, I would have the mbbi record scan disabled by mbbo.PACT Here the database. -> is a PP link or a forward link. The input link from mbbo2.SDIS to mbbi.PACT is not shown. The input link from mbbi.SDIS to mbbo.PACT is also not shown. (ai) is the same record as ai, reproduced in the diagram so I don't have to try to show a link going back to the ai record. mbboCalc is a calcout record, which has a conditional output link programmed to write only if its input value is (the numeric equivalent of) "low" or "high". It's ok if ao and ai are asynchronous. ai -> mbbiCalc -> mbbi -> mbb0 -> mbb02 -> mbboCalc -> ao -> (ai) Here's the sequence of events when a CA or database put writes to mbbo: 1) mbbo writes to mbbo2 2) mbbo2 writes to mbboCalc 3) mbboCalc writes to ao (if mbbo2.VAL is "low" or "high") 4) ao writes to the device and forward links to ai 5) ai reads from the device and writes to mbbiCalc 6) mbbiCalc writes to mbbi 7) mbbi is scan disabled by mbbo.PACT Here's the sequence of events when a CA or database put writes to ao: 1) ao writes to the device and forward links to ai 2) ai reads from the device and writes to mbbiCalc 3) mbbiCalc writes to mbbi 4) mbbi writes to mbbo 5) mbbo writes to mbbo2 6) mbbo2 is scan disabled by mbbi.PACT Tim Mooney ([email protected]) (630)252-5417 Beamline Controls & Data Acquisition Group Advanced Photon Source, Argonne National Lab. Emmanuel Mayssat wrote: I have been struggling with a record loop. What is the best way to implement the following.
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ANJ, 02 Sep 2010 |
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