piclist 2001\03\08\105934a >
Thread: 16F628
www.piclist.com/techref/microchip/devices.htm?key=16F
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face BY : Mike Mansheim email (remove spam text)



> I am running this chip in the internal 4Mhz mode. I am looking at RA1
> with an input signal train swinging between 0 & 3 volts as observed on
> a CRO. I cannot get the program to recognise a high level. The chip is
> powered from 5 volts.

I worry that I'm missing something when a reason seems simple, but...
According to the 16F628 data sheet, RA1 is a schmitt trigger input, which
means an input high must be at least 0.8Vdd, which would be 4V.  So the
3V simply isn't high enough.
Note that this is different from a chip that I use a lot (F87x), where
most of portA, including RA1, are TTL inputs, where the 3V would be a
logic high.

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