>----------
>From:  Scott Horton[SMTP:Scott.Horton1@BRIDGE.BST.BLS.COM]
>Sent:  Tuesday, December 03, 1996 2:16 PM
>To:    Multiple recipients of list PICLIST
>Subject:       Hardware Question 16C84
>
>(snip)
>1. Can someone tell me (in laymen terms?) what a Schmitt Trigger
>is/does/is used for (as shown in the 16C84 notes)?

A Schmitt Trigger is basically a gate with hysteresis (sp?). For
example, a normal gate may turn on at 2.5 volts on the input. It will
also turn off at that value. An input voltage that does not move quickly
through that 2.5 volt point may cause the output to oscillate. Not nice.
Normal digital type signals don't have that problem (they have a fast
rise time), but interface signals from the outside world may not have
this fast rise time. A Schmitt trigger uses positive feedback to cause
the output to switch rapidly once the input reaches the trigger level.
And it won't switch back unless the input voltage drops to a value
somewhat lower than the initial trigger value. For example, it the
output might go high when the input reaches 2.5 volts, and will switch
rapidly. It will stay high until the input voltage goes to 2 volts.
(These are just made-up numbers to show the idea).

So in the case of the PIC pins, those with a Schmitt trigger input can
safely be driven by signals
that have a slowly rising (or dropping) waveform, (such as a sine wave),
and the PIC will just see a fast transition from low to high, or high to
low.
>
(SNIP)

Larry