From: Spehro Pefhany
Subject: Re: RS232 newbie - in need of assistance!
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Date: Fri, 03 Jan 2003 21:35:50 GMT
NNTP-Posting-Date: Fri, 03 Jan 2003 16:35:50 EST
On Fri, 3 Jan 2003 22:03:00 +0100, the renowned "PCS Electronics"
>Will the output pin be OK, if he programs it as an output and than
>shorts it down to gnd with a switch? What happens if a brown-out
>occurs and mcpu starts runnning erratic code?
Shorting an output to ground won't usually cause enough dissipation
to hurt the chip at room temperature. Source current in constant
current mode is less than sink current.
>I'm pointing this out because someone in this NG said a while ago
>that a PIC can source enough current to drive a LED, connected to
Oh, probably 50mA or so typical, which is above the abs. max. 25mA,
but it won't kill it for a short period of time under "typical"
>I don't know about PIC, but AVR can be programmed to have internal
>pull-ups activated, rendering pull-ups unnecessary.
Some pins on some PICs have them.
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.
"it's the network..." "The Journey is the reward"
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