Am Donnerstag, 5. April 2007 14:31 schrieb Rob Conway:
>
> NOW MY PROBLEM
> The digital input board uses DS2405 and I just read the sense parameter.
> It seems that regardless of how fast I scan these (2 sec or 20 sec) it
> takes 2 (sometimes 3) reads of the sense parameter before the state
> changes. Again if I physically turn off the input, the 1st read no change
> the 2nd read it will show a change.
>
> I am now approaching 20 devices on the network and do not particulary want
> to scan these Digital inputs twice as fast as nessecary. I am going to use
> some inputs as "momentary buttons and a high level alarm" thus wanting to
> read the status on every scan.
>
Aside from using a microcontroller as the host, the DS2405 is unsuitable for
momentary buttons. To catch a single keypress, you have to scan right at the
moment the key is pressed. With a multi-process OS like Linux, this is not
feasible. It's likely your application is currently suspended due to some
other process occupying the processor, so you lose the keypress.
Other problems like key chatter get in your way, too.
Use the DS2408 as a keyboard input. It has internal edge detector and latches,
and a alarm function triggered as soon as an edge is detected. With this
chip, you eleminate the problems you have with the DS2405 and may use the
conditional search function (alarm directory) to check if any button was
pressed since last check.
Kind regards
Jan
--
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is to make a copy of everything before he destroys it.
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