[sdiy] 4006 on evilBay

[Tom Wiltshire]

On 12 Feb 2011, at 10:50, Colin f wrote:

> 
>> Some PICs have an open drain output too, so you can do the 
>> level shift without adding the transistor. 
> 
> Are you sure about that, Tom ?

Well, not absolutely certain, I suppose. It was my understanding that that was what the open drain outputs were intended for, but I've got the stick by the sticky end enough times before now that I wouldn't claim infallibility.

> With a GPIO pin in OD, I still don't think you can exceed Vdd + 0.7v or the
> protection diodes kick in.

I don't think the open drain outputs count as standard GPIO. If you look at the datasheet for the PIC 16F627A (just an example - I know this chip has an OD output) the diagram (fig 5-4) for the RA4 port pin shows no protection diode to Vdd, only Vss. So it looks to me like you can pull it up to whatever voltage you like. Compare with the other pins, which have both diodes.

http://ww1.microchip.com/downloads/en/devicedoc/40044d.pdf

T.