PIC sinking voltages higher that Vdd???

[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.

[keithdoxey]

Hmmm...interesting this one.

Just looked at the datasheets on my PC for 16F84, 16F628 and 16F628A

The 84 doesnt show diodes but mentions them and specifically says that RA4 is open drain and only has a diode to VSS. It also says that the maximum voltage on any pin is VDD +0.6v except MCLR wich is 14V

The datasheets I have for 628 and 628A both SHOW a diode on RA4 to VDD but also show it as an open drain pin. The spec says max voltage on any other pin is VDD + 0.3V EXCEPT MCLR AND RA4 which are 14V

Obviously something is not right in the datasheet and I would suspect that the diod ISNT present. My understanding of having an open drain pin is specifically to allow it to sink a load driven from a higher voltage hence the electrical spec stating 14V maximum. If the diode IS present then you wont be able to do that.

[Ioannis]

So, if one is in doubt, take the multimeter and check for a diode on pin RA4 to Vdd!

Ioannis

[keithdoxey]

So, if one is in doubt, take the multimeter and check for a diode on pin RA4 to Vdd!

Ioannis

Or put a 10k resistor between RA4 and +12v and measure the voltage.

If its 12v then no diode, if its 5.3-5.6 then there is a diode.

[Acetronics2]

So, if one is in doubt, take the multimeter and check for a diode on pin RA4 to Vdd!

Ioannis

How much current does your multimeter use for the test ??? more or less than 500µA ???

Good question ...

Alain

[Ioannis]

Hmm, few times I 've placed PIC's reverse direction on their sockets and thay got hot but not destroyed! Of course to be sure these PIC's are only in the lab for testing and never used for a commercial product...

Ioannis

[manumenzella]

Hey. Thanks for your answers. I have no idea how much current my multimeter uses to test for diodes....
Yeah, ssame here. If yuou connected the other way round, the just get hot, but they dont fry
I suspect their life could be shorten, though....
Thanbks again.
Manuel

PS I think i will use PA.4. Thanks for your help!!!