For more output current drive, can I parallel the outputs of a PIC chip port? Assume the pins are all on the same port (e.g., RC0-RC7) and that my firmware will never accidentally drive individual pins to unequal values.
Yes. It's a good idea. Remember not to exceed port and total IC output current limits (in the data sheets).
Cheers Chris
Thanks, Chris. It seemed like it should work, but a second opinion is reassuring.
I think you would be better off using a unity gain amp or depending on what you need for example, a sink output ? just pass the output via a resistor to the base of a npn common emitter style config. Use the collector as your sink driver.. Of course, you'll need to invert the logic of your output in the code.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
I need a source output. Basically I want to power an op amp and some sensors, so I can shut them down when the PIC is in sleep mode. Is there a drawback to running the output pins in parallel, that justifies the additional components for an external transistor?
Unless you're limiting yourself to SETF and CLRF statements, if you happen to leave one output 0 when all others are 1. say goodbye to your micro.
How many chips are you prepared to lose during the debugging process?
"Oops, that was supposed to be MOVF PORTB, W not MOVWF PORTB", as a wisp of smoke rises from your circuit...
Hi, Randy. Assuming the OP is paralleling outputs to drive a resistive load, he could use current limiting resistors at each output to help during the debugging process, like this (view in fixed font or M$ Notepad):
| | .------. .-------. | | | | | ___ | | o--. | o-|___|---. | | | | | | | 270 | | | | | | ___ |/ | | ___ | |/ | | o--o-|___|--| = | o-|___|---o-| | | PIC | | 100 |> | PIC | 270 | |>
| | | | | | | ___ | | | | o--' === | o-|___|---' === | | | GND | | 270 GND | | | | | | '------' '-------' | | (created by AACircuit v1.28.6 beta 04/19/05
You have a very good point -- the OP should do everything he can to protect his development system from himself. ;-)
Cheers Chris
Very true; for a one-off hobby project, that might work. With a bit of experimentation, he'd even be introducing himself to digital/analog conversion.
But for the cost of the extra resistors, he could upgrade to a Darlington transistor, and only need one output pin.
Thanks for the helpful tips! I think that for this application, I should do my initial debugging with the series resistors. My program will be using the SETF and CLRF statements, but still, protecting myself from my stupid mistakes sounds prudent.
Your INITIAL debugging? Once you add the resistors, you're pretty much stuck with 'em. Think about it; how can you be sure that, in some dark corner of your otherwise working code, some instruction was only prevented from zapping the micro *because* the resistors were there.
Once you take them out...
Build with, or build without, there is no ... okay, enough with the Yoda impersonation. :P
One other point to consider; do you think you might expand the project at a later time? Add some new functionality? Maybe you need more i/o pins that, (drat!) are used up now.
I still don't think joining outputs is an optimal solution. Just my opinion.
Points well taken.
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