From: Spehro Pefhany
Subject: Re: RS232 newbie - in need of assistance!
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Date: Fri, 03 Jan 2003 22:43:03 GMT
NNTP-Posting-Date: Fri, 03 Jan 2003 17:43:03 EST
On Fri, 3 Jan 2003 23:03:41 +0100, the renowned "PCS Electronics"
>"Spehro Pefhany" wrote in message news:email@example.com...
>> On Fri, 3 Jan 2003 22:03:00 +0100, the renowned "PCS Electronics"
>> BTW, he should be careful of RA4 with a software UART on the other
>> port A pins. For example, setting the data output pin high could
>> cause the LED to turn on and stay on.
>> This can be prevented by adding some software, using a PORTB pin,
>> by adding a pullup resistor, or by using a red LED rather than
>> some other colors (maybe). ;-) Incantations and sprinkling with
>> holy water have proven ineffective against this.
>That's a weird issue. But he did in fact have this pull up bofore, 100K.
>Probably copied it from a similar design. I advised him, in lack of a better
>judgement, to remove it. So, you're saying the LED won't go off if he takes
I missed that- yes, it was probably a dubious fix that someone did.
It *will* go off, but it *might* come back on again when a different
port bit is written to. The 100K is a oui bit high too, because of
the RC product with stray and LED capacitance and the drain
capacitance, not because of leakages, depending on the microcontroller
clock frequency, of course. 10K would be much better, probably should
be lower if he was running at 20MHz for the results to be completely
code independent. Depends on how many cycles there are between the
write and RMW instructions such as bcf/bsf whether the "off" will
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