On Mon, Mar 08, 1999 at 12:14:22AM -0800, Gerhard Fiedler wrote:

> in my data sheets of all the 16c7x series it says "the trisa register
> controls the direction of the ra pins, even  when they are being used as
> analog inputs" in the porta chapter, and "the port pins that are desired as
> analog inputs must have their corresponding tris bits set. if the tris bit
> is cleared, the digital output level (Voh or Vol) will be converted" in the
> adc chapter.
>
> i read this as that the output level will actually be a digital one (Voh or
> Vol) in case the tris bit is cleared (which is consistent with the
> schematic of the porta inputs in the data sheets). do you read something
> different here?

Well, at no point does it actually say that if the TRIS bit is cleared will
the digital output level appear on the pin; the statement about "the output
level will be converted" means that the analog input will see the digital output
,
but says nothing about what will appear on the external pin.

Certainly nothing in the text is a clear assurance that with TRIS cleared the
pin will work as an output, OTOH I agree with you that the logic diagram does se
em
quite clear; but I know that in practice, I found it not to work. Also remember
that the logic diagram is illustrative only, and is not the actual circuit.

If I get time, I'll run some tests again, just to get to the bottom of this.

Cheers, Clyde

--
Clyde Smith-Stubbs               |            HI-TECH Software
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