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#22106 - 09/07/10 11:04 PM Get Latched -vs- Get Real Time I/O
John Hughes Offline
newbie


Registered: 06/14/10
Posts: 8
What is the difference between the Get Latched I/O and Get Real Time I/O commands?

They appear to both work with the SECU16, SECU16I, & RLY08-XA modules and according to the docs they seem to return some of the same data (ie, both return latched relay bits).

I guess what I don't understand is what is the difference between "Latched Input Bits" and "Real Time Input Bits"... those seem to be the only difference in the docs.

Thanks

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#22107 - 09/08/10 05:12 AM Re: Get Latched -vs- Get Real Time I/O [Re: John Hughes]
Guy Lavoie Administrator Offline
Beyond All Hope
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Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
The difference is as follows:

The bus polling routine of the controller systematically polls each module to see if any inputs have changed. Depending on the number of modules on the bus, there can be any interval from just a few hundreths of a second to a second or more between polls of the same module. Just sending an IR code to a SECU16IR can monopolize the bus for about one second. During that time a module like the SECU16 might receive very short input events, like someone pressing a button for a half second, which might happen between two polls of the module's status. To avoid "missed" input events like that, the module latches ("remembers") if a supervised input went from off to on from one poll to another. If an input did go on, it will return a "on" status for that input even if it is now off again at polling time. That is the latched status. Getting real time status would just return the current status of the inputs, regardless of what might have happened between polls.
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#22108 - 09/08/10 08:08 AM Re: Get Latched -vs- Get Real Time I/O [Re: Guy Lavoie]
John Hughes Offline
newbie


Registered: 06/14/10
Posts: 8
So when using "latched" if an input goes ON, OFF, ON, OFF between polls then will the next 4 "Get Latched I/O" polls return ON,OFF,ON,OFF (while "Get RealTime I/O" would just return OFF?

In other words when I use "Get Latched I/O" repeatedly will it return all the missed state changes or just the prior one?

In the Elve driver I would assume I would want to send the "Get Latched I/O" command at timed intervals... is there a recommended interval?

Thanks,
John

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#22109 - 09/08/10 06:18 PM Re: Get Latched -vs- Get Real Time I/O [Re: John Hughes]
Guy Lavoie Administrator Offline
Beyond All Hope
*****

Registered: 12/21/02
Posts: 6548
Loc: Montreal, QC, Canada
No, it only returns one "on", no matter how many actually times this occurred between the current and the previous status polls.
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"If you don't know what you're doing, do it neatly..."

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