Am Donnerstag, 9. August 2007 07:02 schrieb Gregg C Levine:
> Hello!
> Paul, David, (welcome to the group by the way.), the DS2423 counter chip is
> a strange animal. It requires an external power supply to run it.
>
The RAM is not 1W powered, but Vdd powered only. So Vdd acts as an -RESET
input, too.
> Also it
> requires specialized devices attached to its counter inputs, the data sheet
> specifies them, but essentially a mechanical reed switch will do that.
>
For speed reasons the counter inputs have *no* Schmitt trigger! That means, if
you leave the inputs open, they will float to about 1/2 Vdd and count the
athmosperic noise in the meantime. To avoid this, one have to pullup the
input with an resistor to Vdd. This is not done internally as such a resistor
either limits counting speed or presents too low input impedance -- and it's
just not needed for connecting the usual push-pull outputs, just for
switches.
Kind regards
Jan
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