Jim Thompson wrote:
On Thu, 11 Mar 2010 09:07:43 -0800, Tim Wescott
wrote:

Jim Thompson wrote:
When a uP or uC is exercising its POR cycle, what are the states of
the output pins? Floating, or held low, or what?

Particularly if it's recovering from a brown-out that caused POR to be
exerted.
You do mean _output_ pins, not general purpose I/O that might be
configured for either input or output -- right?

I guess I could be driven by an I/O pin. Is it possible to program
those as a "LOW" during POR?

What are you _really_ trying to do?

I gather that you want to drive some bit of circuitry during POR, but
for some reason you can't just monitor the reset line. Do you want to
_drive_ it or do you just want to signal that a reset is occurring?

_Some_ microcontrollers will drive their outputs to some defined state,
or will put weak pull-up or pull-down devices on their GPIO pins during
POR. If you don't mind the low speed and low current capability, you
could use one of these 'weak pull-up' pins to indicate a reset, then
have software clear the pin when it wakes up.

If you're trying to make some generic peripheral that'll work on every
microprocessor in existence, and have the correct POR behavior, you're
screwed -- none of them act the same, and (as I think you've pointed out
yourself) not all of them even behave _appropriately_ in response to a
brownout event.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com