Tilmann Reh <tilmannreh@despammed.com> wrote:

>Joop schrieb:
>
>> Hmm, 
>> 1) your 8051 has an internal WDT
>> 2) you reserved an output pin (to hush the WD)
>> 
>> Why not shake this pin by the micro right after a reset? Essentially
>> making it function as the circuit you asked for.
>
>Hmm,
>
>you don't know how the internal WD (of those few 8051 which have one)
>works.
>(It is triggered by a sequence of accesses to internal registers, not
>by an externally applied signal.)
>Additionally, the OP asked for power-up/down reset, too.

Yes, but the OP did not mention time critital requirements.
When the 8051 resets (either at power-on or WDT intervention) it is
possible to execute the necessary instructions to pull the output pin
low or high for some time. 
Just put them in the startup code, perhaps even before setting the SP
and other usual startup code.

The external circuitry gets reset a little later than the 8051 itself,
but the OP did not give an indication this might be a problem.

As for hushing the WDT, the OP also did not mention it should be
hushed by external circuitry. Only that the external stuff should be
reset.
Of course if external devices do need this, than things would be
different as you seem to be assuming. 
This might still be done by connecting the external 'hush-signal' to
an additional 8051 (interrupt) pin and put some WDT code behind it.

Joop

Joop schrieb:

> Hmm, 
> 1) your 8051 has an internal WDT
> 2) you reserved an output pin (to hush the WD)
> 
> Why not shake this pin by the micro right after a reset? Essentially
> making it function as the circuit you asked for.

Hmm,

you don't know how the internal WD (of those few 8051 which have one)
works.
(It is triggered by a sequence of accesses to internal registers, not
by an externally applied signal.)
Additionally, the OP asked for power-up/down reset, too.

-- 
Dipl.-Ing. Tilmann Reh
Autometer GmbH Siegen - Elektronik nach Ma�.
http://www.autometer.de

edaudio2000@yahoo.co.uk (ted) wrote:

...
>know the 8051 has an internal WDT circuit, but this is in addition as
>the reset signal is needed elsewhere).
>
..
Hmm, 
1) your 8051 has an internal WDT
2) you reserved an output pin (to hush the WD)

Why not shake this pin by the micro right after a reset? Essentially
making it function as the circuit you asked for.

Joop  

On Thu, 28 Oct 2004 09:44:29 +1300, the renowned Jim Granville
<no.spam@designtools.co.nz> wrote:

>Joerg wrote:
>> Thanks to both of you. I didn't know they entered the 25c range by now. 
>> I couldn't find the LM3700 this low but I am sure it is possible. The 
>> STM706 is fixed 5V so it's not that useful. Now I just wish ST had a 
>> better web site where one can quickly find a part against a budget price.
>
>If ST's web site drivs you to distraction, a better web portal is
>OnSemi's - eg
>
>http://www.onsemi.com/site/products/summary/0,4450,NCP300,00.html?tax=694
>
>Shows Reel prices of 14.2c, and appx 500nA operate - apps also show how 
>to use these as low-ish power oscillators, like a new '555....
>-jg

These lack the timer feature, however. They are just voltage
detectors. The 0.5uA consumption is very nice. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Joerg wrote:
> Thanks to both of you. I didn't know they entered the 25c range by now. 
> I couldn't find the LM3700 this low but I am sure it is possible. The 
> STM706 is fixed 5V so it's not that useful. Now I just wish ST had a 
> better web site where one can quickly find a part against a budget price.

If ST's web site drivs you to distraction, a better web portal is
OnSemi's - eg

http://www.onsemi.com/site/products/summary/0,4450,NCP300,00.html?tax=694

Shows Reel prices of 14.2c, and appx 500nA operate - apps also show how 
to use these as low-ish power oscillators, like a new '555....
-jg

Hi Spehro,

>The LM809/MCP809 (note that the pinout is different) is/are cheaper
>but don't have the /NMI output. 
>  
>
That is a nice chip. Only fixed voltages but the versions come in 
sufficient granularity. Doesn't beat the discrete solution if there is a 
1.2V reference for other purposes, but it does if there isn't.

>>STM706 is fixed 5V so it's not that useful. Now I just wish ST had a 
>>better web site where one can quickly find a part against a budget price.
>>
>>In a few years this issue should be behind us when all uCs have on board 
>>BOR features that work well.
>>    
>>
>
>I'm almost afraid to ask Jim how it's going... 
>  
>
Jim Thompson? Did he design some of these?

Regards, Joerg

http://www.analogconsultants.com

On Wed, 27 Oct 2004 18:31:28 GMT, the renowned Joerg
<notthisjoergsch@removethispacbell.net> wrote:

>Hi Jim, Hi Spehro,
>
>>> National's versions of Microchip's parts. 
>>
>>
>>  And also STm have entered this market,
>> http://www.st.com/stonline/press/news/year2004/p1510m.htm
>>
>> Now the big analog players are there, prices should be more sensible,
>> and most new uC releases have these Power Monitoring features inbuilt.
>
>Thanks to both of you. I didn't know they entered the 25c range by now. 
>I couldn't find the LM3700 this low but I am sure it is possible.

The LM809/MCP809 (note that the pinout is different) is/are cheaper
but don't have the /NMI output. 

>STM706 is fixed 5V so it's not that useful. Now I just wish ST had a 
>better web site where one can quickly find a part against a budget price.
>
>In a few years this issue should be behind us when all uCs have on board 
>BOR features that work well.

I'm almost afraid to ask Jim how it's going... 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Hi Jim, Hi Spehro,

>> National's versions of Microchip's parts. 
>
>
>  And also STm have entered this market,
> http://www.st.com/stonline/press/news/year2004/p1510m.htm
>
> Now the big analog players are there, prices should be more sensible,
> and most new uC releases have these Power Monitoring features inbuilt.

Thanks to both of you. I didn't know they entered the 25c range by now. 
I couldn't find the LM3700 this low but I am sure it is possible. The 
STM706 is fixed 5V so it's not that useful. Now I just wish ST had a 
better web site where one can quickly find a part against a budget price.

In a few years this issue should be behind us when all uCs have on board 
BOR features that work well.

Regards, Joerg

http://www.analogconsultants.com

On Wed, 27 Oct 2004 00:42:14 GMT, the renowned Joerg
<notthisjoergsch@removethispacbell.net> wrote:

>Hi Spehro,
>
>>>Actually with an LMV431 you can make a really accurate yet cheap voltage 
>>>detector. This little part is under 20 cents. I really don't know why 
>>>brown-out/reset chips are so expensive. So I am just not using them in 
>>>my designs until that changes.
>>>    
>>>
>>
>>They're not anymore. Now they are available for 25 cents or so, one
>>reel quantity, with tightly guaranteed trigger voltage plus a
>>reasonable time delay. I think that's a no-brainer if you need such a
>>device.
>>
>25 cents sounds like a good deal. Which one is that?

National's versions of Microchip's parts. 


Best regards, 
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

Spehro Pefhany wrote:
> On Wed, 27 Oct 2004 00:42:14 GMT, the renowned Joerg
> <notthisjoergsch@removethispacbell.net> wrote:
> 
> 
>>Hi Spehro,
>>
>>
>>>>Actually with an LMV431 you can make a really accurate yet cheap voltage 
>>>>detector. This little part is under 20 cents. I really don't know why 
>>>>brown-out/reset chips are so expensive. So I am just not using them in 
>>>>my designs until that changes.
>>>>   
>>>>
>>>
>>>They're not anymore. Now they are available for 25 cents or so, one
>>>reel quantity, with tightly guaranteed trigger voltage plus a
>>>reasonable time delay. I think that's a no-brainer if you need such a
>>>device.
>>>
>>
>>25 cents sounds like a good deal. Which one is that?
> 
> 
> National's versions of Microchip's parts. 

  And also STm have entered this market,
http://www.st.com/stonline/press/news/year2004/p1510m.htm

Now the big analog players are there, prices should be more sensible,
and most new uC releases have these Power Monitoring features inbuilt.

-jg