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Jim Thompson
Guest
Thu Mar 11, 2010 5:42 pm
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.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at
http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Vladimir Vassilevsky
Guest
Thu Mar 11, 2010 5:52 pm
Jim Thompson wrote:
Quote:
When a uP or uC is exercising its POR cycle, what are the states of
the output pins? Floating, or held low, or what?
All bidirectional pins *typically* configured as inputs to avoid
conflicts. However this is NOT a rule. Always check with datasheets.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Tim Wescott
Guest
Thu Mar 11, 2010 6:06 pm
Jim Thompson wrote:
Quote:
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.
That depends on the part.
I have yet to run across a chip with a pin designated as 'output' that
isn't low impedance all the time, but I would expect that whether it is
low, high, or oscillating randomly would depend on the part.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Tim Wescott
Guest
Thu Mar 11, 2010 6:07 pm
Jim Thompson wrote:
Quote:
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?
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Vladimir Vassilevsky
Guest
Thu Mar 11, 2010 6:16 pm
Tim Wescott wrote:
Quote:
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.
That depends on the part.
I have yet to run across a chip with a pin designated as 'output' that
isn't low impedance all the time,
Tip: Open drain
VLV
Michael A. Terrell
Guest
Thu Mar 11, 2010 6:35 pm
Vladimir Vassilevsky wrote:
Quote:
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.
That depends on the part.
I have yet to run across a chip with a pin designated as 'output' that
isn't low impedance all the time,
Tip: Open drain
AFTER your boat is out of the water...
--
Lead free solder is Belgium's version of 'Hold my beer and watch this!'
Tim Wescott
Guest
Thu Mar 11, 2010 6:40 pm
Vladimir Vassilevsky wrote:
Quote:
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.
That depends on the part.
I have yet to run across a chip with a pin designated as 'output' that
isn't low impedance all the time,
Tip: Open drain
Well, yes, but that'll be mentioned. Like you said: read the data sheet.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Nico Coesel
Guest
Thu Mar 11, 2010 7:02 pm
Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
Quote:
When a uP or uC is exercising its POR cycle, what are the states of
the output pins? Floating, or held low, or what?
Preferably in a state as specified in the datasheet.
--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico_at_nctdevpuntnl (punt=.)
--------------------------------------------------------------
Jim Thompson
Guest
Thu Mar 11, 2010 8:11 pm
On Thu, 11 Mar 2010 09:07:43 -0800, Tim Wescott <tim_at_seemywebsite.now>
wrote:
Quote:
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?
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at
http://www.analog-innovations.com | 1962 |
The only thing bipartisan in this country is hypocrisy
Tim Wescott
Guest
Thu Mar 11, 2010 8:20 pm
Jim Thompson wrote:
Quote:
On Thu, 11 Mar 2010 09:07:43 -0800, Tim Wescott <tim_at_seemywebsite.now
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
Hal Murray
Guest
Thu Mar 11, 2010 8:28 pm
Quote:
I guess I could be driven by an I/O pin. Is it possible to program
those as a "LOW" during POR?
Read the data sheet.
In general, the junk I/O pins float. You can't "program" them
from software during reset because the software isn't running yet.
Some chips look at a few input pins to select a mode. Some modes
might drive some pins.
The normal trick is to add a weak pulldown if you need a
particular floating signal to be low during reset.
--
These are my opinions, not necessarily my employer's. I hate spam.
Jim Thompson
Guest
Thu Mar 11, 2010 8:33 pm
On Thu, 11 Mar 2010 11:20:11 -0800, Tim Wescott <tim_at_seemywebsite.now>
wrote:
Quote:
Jim Thompson wrote:
On Thu, 11 Mar 2010 09:07:43 -0800, Tim Wescott <tim_at_seemywebsite.now
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.
That's what I'm concluding. I've found a way to cope with a floating
input that I'm adding into the design
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at
http://www.analog-innovations.com | 1962 |
The only thing bipartisan in this country is hypocrisy
Spehro Pefhany
Guest
Thu Mar 11, 2010 9:20 pm
On Thu, 11 Mar 2010 09:42:29 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:
Quote:
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.
...Jim Thompson
Most microcontrollers float their I/O pins (various possibilities as
to what is connected inside, could be ST digital input could be an
inverter digital input, could be analog circuitry) while the reset is
active.
Since most of them can be configured as either an input or an output,
it's safest to have them power up as inputs so they don't do silly
things like turning motors on or relays if reset is held active.
Sometimes they have internal programmable pull-ups or pull-downs, but
they often don't get configured as such until the user program runs
for a bit.
A few older ones might do interesting things like become
pseudo-birectional outputs with high frequency signals on them.
Michael A. Terrell
Guest
Thu Mar 11, 2010 9:25 pm
Hal Murray wrote:
Quote:
I guess I could be driven by an I/O pin. Is it possible to program
those as a "LOW" during POR?
Read the data sheet.
What if it hasn't been written yet?
--
Lead free solder is Belgium's version of 'Hold my beer and watch this!'
Hal Murray
Guest
Thu Mar 11, 2010 11:11 pm
Quote:
Read the data sheet.
What if it hasn't been written yet?
Why are you designing something for a chip that doesn't exist?
Ask the guy who is trying to sell you the chip?
Ask the guy who told you about the chip?
Use another chip.
--
These are my opinions, not necessarily my employer's. I hate spam.
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