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 | |
| Voice480)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.

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?

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

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, 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

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?

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

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

VLV

Vladimir Vassilevsky wrote:

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!'

Vladimir Vassilevsky wrote:


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

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?

...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 | |
| Voice480)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

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

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.

On Thu, 11 Mar 2010 11:20:11 -0800, Tim Wescott
wrote:

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.

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 | |
| Voice480)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

On Thu, 11 Mar 2010 09:42:29 -0700, 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.

...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.

Hal Murray wrote:

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!'

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.

Hal Murray wrote:

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.


Jim designs chips. There are no data sheets until the designs are
complete.


--
Lead free solder is Belgium's version of 'Hold my beer and watch this!'

On Thu, 11 Mar 2010 18:55:21 -0500, "Michael A. Terrell"
wrote:


Hal Murray wrote:

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.


Jim designs chips. There are no data sheets until the designs are
complete.

I don't design uP's or uC's, at least not complete ones... small local
controls, occasionally.

Here I have a analog situation where a floating input can cause high
currents (like 250mA) to flow, so I just wanted to make sure it was a
real problem before I added-in a fix. It's done, took me 4 MOS
transistors :-)

...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 | |
| Voice480)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

Jim Thompson wrote:

On Thu, 11 Mar 2010 18:55:21 -0500, "Michael A. Terrell"
wrote:


Hal Murray wrote:

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.


Jim designs chips. There are no data sheets until the designs are
complete.

I don't design uP's or uC's, at least not complete ones... small local
controls, occasionally.

Here I have a analog situation where a floating input can cause high
currents (like 250mA) to flow, so I just wanted to make sure it was a
real problem before I added-in a fix. It's done, took me 4 MOS
transistors :-)


I thought you had done some analog parts of ASIC that had a stock CPU
design?


--
Lead free solder is Belgium's version of 'Hold my beer and watch this!'

In message , Michael A. Terrell
writes
Jim designs chips. There are no data sheets until the designs are
complete.
Yeah, but in this case, he's designing what sounds like a peripheral for
an existing chip. If it was a design of Jim's then I'd not have expected
him to need to ask the question.



--
Clint Sharp

On Mon, 15 Mar 2010 19:40:55 +0000, Clint Sharp
wrote:

In message , Michael A. Terrell
writes
Jim designs chips. There are no data sheets until the designs are
complete.
Yeah, but in this case, he's designing what sounds like a peripheral for
an existing chip. If it was a design of Jim's then I'd not have expected
him to need to ask the question.



Ever hear of flaky (*) customers? Many weird, non-physical requests
and lots of misinformation. So I ask here to get the true scoop :-)

* Like a customer who labels the R and C for a triangle wave
oscillator on his "specification" as "TANK1" and "TANK2"... I kid you
not :-(

...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 | |
| Voice480)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