PIC sinking voltages higher that Vdd???

[skimask]

Hey. Thanks for all the answers. I think im going to connect a npn transistor as most of you suggested. The probem is that, as it is battery powered, i need to keep the current draw very small. Do you know which will be (more or less) the current flowing from the IO to the base of the npn???
I was going to use the multimeter to measure it, but, after the cleaning lady came home, the screen was broken into pieces!!!
Well, thanks again for your help
Manuel

Using a transistor instead of a MOSFET is going to cost you a few mA in base current right there. MOSFET's have practically no gate current, generally in the pico-amps (except when switching states due to gate capacitance). Use an N channel MOSFET, 2N7000. It'll easily handle 12v across the drain-source, and switch on/off with 5v logic levels on the gate.

[sougata]

Hi,

Some PICs have an open drain output (say PORTA.4). This means that it has only the lower side N-Channel MOSFET inside. And according to a Microchip FAE this can tolerate upto 8 volts safely. Hopefully it should not be a problem with your buzzer and 9v battery.

[Darrel Taylor]

And according to a Microchip FAE this can tolerate upto 8 volts safely.

You're right, it does say that. But it also says that PORTA.4 has protection diodes to VDD and VSS.

Which one are we supposed to believe?

I suppose a little testing would tell.
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[skimask]

You're right, it does say that. But it also says that PORTA.4 has protection diodes to VDD and VSS.

Which one are we supposed to believe?

I suppose a little testing would tell.
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YES! DESTRUCTIVE TESTING! I LOVE IT!
I've pulled 9v at about 5mA thru A.4 before, don't know if it was determental to the chip or not, but it seemed to work while I was doing it and I am still using the chip.

On the same note, I'm in Tucson, Az. for another couple of weeks. Man is it dry down here! I'm getting some killer static shocks from the doorknob! zzzztttt

[mister_e]

so nobody else use 2 i/o to double the voltage around those cuties?

EDIT : Aw crap... we talked about piezo buzzer right... not sounder... sorry

unless you want to heard something different than it's suppose to be... forget it

[paul borgmeier]

But it also says that PORTA.4 has protection diodes to VDD and VSS.

Which one are we supposed to believe?

Figure 5.4 in the datasheet for the 16F628 shows no clamp diode to VDD.

[Darrel Taylor]

This figure 5-4 ?


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[sougata]

Hi,

This one is from a PIC18F452 datasheet page 90. Note that I/O pin has protection diodes to VSS only.

[Ioannis]

Darrel, take a look at Mid-Range Reference Manual for 16 series. At page 145, Figure 9-3 it clearly states that clamp diode is only to Vss. It could not be otherwise for higer voltage connection. So I suppose the 5-4 you posted might be wrong.

Ioannis

EDIT: Damn, Sougata just got me for a few msec...!

[Darrel Taylor]

Hmmm, well I guess it depends on which PIC you are looking at.
manumenzella never specified. And the original post regarding RA4 as much as assumed they are ALL like that.

Paul was referencing the 16F628, which according to the most recent datasheet, Has the diode.

If you look at a 16F628A, then it doesn't.

If you look at the 18F452 datasheet from a couple years ago, it says it does, but the most recent one doesn't.
Was it a change in the datasheet, or the silicon?

Like my original comment,
"Which one are we supposed to believe?"

Personally, I'd go with the transistor.
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[paul borgmeier]

From an earlier post the OP had

>>Hi. My name is Manuel, and I am building a project around the PIC16F628A and a piezo

http://www.picbasic.co.uk/forum/showthread.php?t=5773

I, in a sloppy manner, left the A off of my reply about the 16F628 datasheet. I had checked the 16F628A sheet and saw no clamp and was just reporting that observation.

However with an actual look at the 16F628 datasheet and the others noted, I see why Darrel asked

>> Which one are we supposed to believe

Great question by Darrel ... here is my version for an answer - if it were a one-off by a school boy intending to rudely disrupt the class room I would go with the 9V on RA4. If it were for a medical device or other lawyer-attacting application, I would go the NPN route and would want a written response from Microchip as an effort to help keep by butt out of court should there ever be a problem before going the non NPN route.