At 01:16 PM 12/3/96 -0600, you wrote:
>Please excuse my weak electronics abilities as I am an ME struggling my
>way into programming these little critters.
>
>I've read (and are still reading) lots of the PIC resources, ECH, FAQ
>archives, etc.  I have a couple of questions I'm sure someone (probably
>everyone but me <g>) can help with:
>
>1. Can someone tell me (in laymen terms?) what a Schmitt Trigger
>is/does/is used for (as shown in the 16C84 notes)?

it means that there is a so called hysteris, ie if input voltge
rises slow and is some noise then after reaching certain level
the schmit trigger output goes to high and stays there until the
input level drops below the lower trigger point. those small noise
in input signal will not produces high to low glitches to be read in.

>2. One of the App Notes from MC - re RS232 interfacing, showed a schematic
>with a component called ZVN104 which was used as part of an interface to a
>RS232 level.  I plan on using a MAX chip or one of the other driver chips
>but I am still curious as to exactly what that component was - for my
>(continuing) education - I was unable to find it with any of my
>electronics suppliers, or at least didn't know what I was looking for :).

in most applications its fair enought to use one 10k resistor to implement
RS232 interface to PIC. PC serial ports accept 0 / +5 Input level signal
and if you put a series resistor for current limiting in TxD line from PC
then the input protection diodes buildt in to PIC16c84 will clamp the
+12/-12V RS232 signal to +5/0 on PIC input pin.

as PIC16C84 does not have hardware uart, so the required serial IO pin
polarity can be adjusted in software.

antti

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