PIC sinking voltages higher that Vdd???

[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!!!