AVR-Chat

On Sun, 21 Oct 2007 16:43:42 -0500
 Thomas Keller <tjkeller1@alltel.net> wrote:
>    So, I have this cute little device I have developed
> for model
> railroaders.  Based on an
> ATtiny25.  Question:  for this device to start
> functioning when the
> power is applied, do I need to connect the *RESET pin
> (pin 1) to something? 
> Perhaps a resistive network to ground, with a small cap
> across the lower 
> (grounded) resistor?
> 
> tom
> 
> 
No...

Unlike the old 8051s and such, the devices, especially with
Brown Out Detection, handle the full "reset on startup" for
you.

Jim


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So, I have this cute little device I have developed for model
railroaders.  Based on an
ATtiny25.  Question:  for this device to start functioning when the
power is applied, do I need to connect the *RESET pin (pin 1) to something? 
Perhaps a resistive network to ground, with a small cap across the lower 
(grounded) resistor?

tom

At 07:43 AM 22/10/2007, you wrote:
>Question:  for this device to start functioning when the
>power is applied, do I need to connect the *RESET pin (pin 1)

Unless you are using the reset pin as an GPIO you could use a
4.7K or 10K pull up and a 100nF cap to ground. Some people just
rely on it's weak internal pull up. You SHOULD also use
the BOD as a reset source and in fact it must be used if the
reset pin is used as I/O.

Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Email: john@ampertronics.com.au
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************

--- In AVR-Chat@yahoogroups.com, Thomas Keller <tjkeller1@...> wrote:

> ... ATtiny25 ... do I need to connect
> the *RESET pin (pin 1) to something?

So, you've had two replies saying the exact opposite things.  I've 
taken a look at the data sheet and it seems clear to me that reset is 
taken care of internally.  I've always relied on the internal reset 
circuits of Atmel microcontrollers and it's always worked fine for me.

Graham.

--- In AVR-Chat@yahoogroups.com, dlc <dlc@...> wrote:
>
> .... I like having an OH S#!% button.

Ah, I didn't mean I don't have an Oh S#!% button.  I invariably do.  I 
just don't have either an external RC network or an external reset chip 
because the internal reset thing seems to work so well.

But, talking of Oh S#!% buttons and drifting wildly off the subject, in 
my day job I'm working at the other end of the spectrum on a BlackFin-
based embedded system running uClinux.  The hardware guys have provided 
no debug inputs or outputs, not even an activity LED on the Ethernet 
port, and, you guessed it, I have to power cycle to reset the thing.

Graham.

<chuckle> And I always use one if I can - I like having an OH S#!% 
button.  But in some designs, such a thing isn't a viable option anyway. 
  With the complexity of the reset circuit that Atmel recommends, if the 
internal reset/startup circuit is reliable you'd save cost using it over 
an external reset circuit.

DLC

Graham Davies wrote:
> --- In AVR-Chat@yahoogroups.com, Thomas Keller <tjkeller1@...> wrote:
> 
> 
>>... ATtiny25 ... do I need to connect
>>the *RESET pin (pin 1) to something?
> 
> 
> So, you've had two replies saying the exact opposite things.  I've 
> taken a look at the data sheet and it seems clear to me that reset is 
> taken care of internally.  I've always relied on the internal reset 
> circuits of Atmel microcontrollers and it's always worked fine for me.
> 
> Graham.
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 

-- 
-------------------------------------------------
Dennis Clark          TTT Enterprises
www.techtoystoday.com
-------------------------------------------------

At 09:23 AM 23/10/2007, you wrote:
>I just don't have either an external RC network or an external reset chip
>because the internal reset thing seems to work so well.

Even if the BOD is disabled? ie one forgets to enable it.

No noise induced into the reset line in noisy environments
like a car that MAY require a more solid pull up and filter
cap?

Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Email: john@ampertronics.com.au
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************

Leave it to John to hit the nail on the head.  My Tiny25 device will be 
in an extremely "noisy"
environment, specifically, inside a model railroad locomotive.  The 
power comes from the rails
(which is itself a noisy pickup source), through a bridge rectifier, 
into a  .01 µF cap, into a 78L05
and into a .1 µF cap, then into the Tiny25 and a pair of switching NPNs 
(BC847s, if anyone cares).

   So, what do you think, John?   I need for this thing to start up 
whenever the locomotive sees
power (it is designed for NMRA DCC (Digital Command and Control) so the 
DC supply level
should be fairly bconstant, between 12 and 18 VDC).  Startup is not 
*CRUCIAL*, if the beacon
doesn't start,m the user can simply lift the locomotive off the track 
and replace it again.   No space
for a 'reset" button, and certainly no space for more than a tiny cap 
and a 1/8th watt resistor.  I would
]prefer that startup be FAIRLY reliable, but again, it is not *CRUCIAL*.

avrFreak

At 09:52 AM 23/10/2007, you wrote:
>I need for this thing to start up whenever the locomotive sees
>power

Enable the Brown Out Detector, this will give you reliable reset
at power up.

The point I'm trying to make is that, if you have a track running
from the reset line, say to the ISP connector, then you have a small
antenna connected to the reset line. With a high resistance in the reset
line like the internal pull up, one is more likely to pick up rubbish
that COULD give you spurious resets. A cap on the reset line will help
with this as well as giving you another reset at power up.

However you SHOULD use the internal BOD at least for better reliability.

I'm fortunate enough that my projects have never been that packed or
price sensitive that I could not put a cap and resistor in the reset line.

Try it without see what happens, I may just be a panic merchant :-)


Regards

John Samperi

********************************************************
Ampertronics Pty. Ltd.
11 Brokenwood Place Baulkham Hills, NSW 2153 AUSTRALIA
Tel. (02) 9674-6495       Fax (02) 9674-8745
Email: john@ampertronics.com.au
Website  http://www.ampertronics.com.au
*Electronic Design * Custom Products * Contract Assembly
********************************************************

--- In AVR-Chat@yahoogroups.com, John Samperi <samperi@...> wrote:

> Even if the BOD is disabled? ...

Actually, yes.  In the MCUs I use, and the ATtiny25, the reset function 
is separate from and in addition to BOD.  You can see this depicted in 
the data sheet (Figure 9-1 in the 12/06 revision).  Separate sections 
describe the POR (Section 9.3) and BOD (9.5) functions.

So, yes, I have shipped product intentionally without BOD enabled.  
There have been no reports of power-up failures.  What does happen 
occasionally, however, is that if power is applied and then removed 
almost immediately (or bounces on the way down) you can lose fuses or 
even Flash data.  *This* is why BOD is so important, not to ensure a 
good power-up reset.

So, I would say that the OP should follow your advice with regard to 
enabling BOD and making sure the reset line is not an antenna but can 
otherwise trust the ATtiny to reset itself on power-up without an 
external RC or reset chip.

Graham.

Is it possible to permanently disable all kinds of read/write operations to the flash?

Regards,

Manne

On Tue, 23 Oct 2007 16:32:33 +0200 (CEST)
 "Manne Tallmarken" <mannet@kth.se> wrote:
> Is it possible to permanently disable all kinds of
> read/write operations to the flash?
> 
> Regards,
> 
> Manne
> 

I don't believe that you can, PERMANENTLY. If the device
can be parallel programmed, the fuses can be over-ridden by
erasing the flash (or something like that). Also, devices
with SPM operation can write to flash, I believe, if it is
run from the proper code space no matter what the fuses are
set to.

That is my understanding of such things.

Jim Wagner
Oregon Research Electronics, Consulting Division
Tangent, OR, USA
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