8051 reset circuit

I m not much of an expert on this side of things, and there are
thousands of reset and power management chips from people like Maxim
out there. It would take me ages to go through all that lot...but as
there are some experts here, I might as well ask!

Can anybody recommend a chip number, or pointer to a discrete circuit
for a reset management chip for an 8051 that will:

a) produce a clean reset pulse on power supply going up and down (I
know they all do this..!)

b) respond to a regular watchdog pulse input from the micro and
produce a reset signal if the pulse is missing for a given time (I
know the 8051 has an internal WDT circuit, but this is in addition as
the reset signal is needed elsewhere).

TIA...

ted

ted schrieb:

> I m not much of an expert on this side of things, and there are
> thousands of reset and power management chips from people like Maxim
> out there. It would take me ages to go through all that lot...but as
> there are some experts here, I might as well ask!
> 
> Can anybody recommend a chip number, or pointer to a discrete circuit
> for a reset management chip for an 8051 that will:
> 
> a) produce a clean reset pulse on power supply going up and down (I
> know they all do this..!)
> 
> b) respond to a regular watchdog pulse input from the micro and
> produce a reset signal if the pulse is missing for a given time

The MAX/DS/TC 1232 is a fairly common chip that has these two functions.
It also has a manual reset (pushbutton) input.

> (I
> know the 8051 has an internal WDT circuit, but this is in addition as
> the reset signal is needed elsewhere).

No. The 8051 does *not* have an internal WD.
Only few (most recent) parts have one.

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

"Tilmann Reh" <tilmannreh@despammed.com> wrote in message
news:cll621$e4v$1@online.de...
> ted schrieb:
>
> The MAX/DS/TC 1232 is a fairly common chip that has these two functions.
> It also has a manual reset (pushbutton) input.

I agree. The MAX1232 is my reset device of choice. I've used it in many
designs with no problems at all.

Steve
http://www.fivetrees.com

Hi Ted,

Whatever you use make sure it also features a good brown-out handling, 
when the voltage doesn't drop to zero but briefly dips under the limit 
needed for stuff to function normally. You can test that on the bench. 
Personally I always roll my own reset with a transistor.

A few newer uC have brown-out features on board, for example some of the 
MSP430.

Regards, Joerg

http://www.analogconsultants.com

Hi Ted,

>b) respond to a regular watchdog pulse input from the micro and
>produce a reset signal if the pulse is missing for a given time (I
>know the 8051 has an internal WDT circuit, but this is in addition as
>the reset signal is needed elsewhere).
>  
>
You can do this with a CD4060. Configure it as an oscillator, tap off at 
the desired divider for time-out and have the uC reset it at prescribed 
intervals. That way you can create a really long timer without low 
leakage caps and all that. The CD4060 comes in the tiny TSSOP package if 
space is an issue.

Regards, Joerg

http://www.analogconsultants.com

On 26 Oct 2004 01:45:20 -0700, the renowned edaudio2000@yahoo.co.uk
(ted) wrote:

>I m not much of an expert on this side of things, and there are
>thousands of reset and power management chips from people like Maxim
>out there. It would take me ages to go through all that lot...but as
>there are some experts here, I might as well ask!
>
>Can anybody recommend a chip number, or pointer to a discrete circuit
>for a reset management chip for an 8051 that will:
>
>a) produce a clean reset pulse on power supply going up and down (I
>know they all do this..!)
>
>b) respond to a regular watchdog pulse input from the micro and
>produce a reset signal if the pulse is missing for a given time (I
>know the 8051 has an internal WDT circuit, but this is in addition as
>the reset signal is needed elsewhere).
>
>TIA...
>
>ted

The ADM805 is a good WDT/reset/power fail supervisory circuit with
active high output (as required for many 8051-type parts). Maxim and
AD make it (and maybe others). 



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 Spehro,

>The ADM805 is a good WDT/reset/power fail supervisory circuit with
>active high output (as required for many 8051-type parts). Maxim and
>AD make it (and maybe others). 
>  
>
Somehow AD always comes to the rescue. My only gripe with this kind of 
stuff is the price, more than $2 for the ADM805. That would be about the 
same as the cost for a middle class uC.

I'd still do it with a home grown reset and something like a 4060 for 
the WD timer. Until some company comes along with a chip that does it 
reliably for about 40 cents or so including any peripheral discretes.

Regards, Joerg

http://www.analogconsultants.com

On Tue, 26 Oct 2004 20:48:35 GMT, Joerg <notthisjoergsch@removethispacbell.net>
wrote:

>Somehow AD always comes to the rescue. My only gripe with this kind of 
>stuff is the price, more than $2 for the ADM805. That would be about the 
>same as the cost for a middle class uC.
>
>I'd still do it with a home grown reset and something like a 4060 for 
>the WD timer. Until some company comes along with a chip that does it 
>reliably for about 40 cents or so including any peripheral discretes.

Exactly!  I've used an HC132 based design for the 80C32's I've used in the past,
built on a tiny smt piggyback for the 8032, which included both power-on and
watchdog features.

Jon

On Tue, 26 Oct 2004 20:48:35 GMT, the renowned Joerg
<notthisjoergsch@removethispacbell.net> wrote:

>Hi Spehro,
>
>>The ADM805 is a good WDT/reset/power fail supervisory circuit with
>>active high output (as required for many 8051-type parts). Maxim and
>>AD make it (and maybe others). 
>>  
>>
>Somehow AD always comes to the rescue. My only gripe with this kind of 
>stuff is the price, more than $2 for the ADM805. That would be about the 
>same as the cost for a middle class uC.

We paid about 90 cents in 1K or 2K for it, IIRC. That was about 5-6
years ago. Maxim never gave quotes that low, so maybe they got some
design-ins and jacked the price up. 

>I'd still do it with a home grown reset and something like a 4060 for 
>the WD timer. Until some company comes along with a chip that does it 
>reliably for about 40 cents or so including any peripheral discretes.

Yeah, it really depends what's required. It would be nice if the
microcontroller on-chip peripherals were both present and good enough
to depend on. If you're not running the chip flat-out speed-wise,
modern MCUs have enough voltage range that a sloppy & cheap voltage
detection circuit will be good enough. The original
pseudo-bidirectional 8051 ports are nasty anyway- reset the chip and
they become outputs and source enough current to turn on an NPN
darlington, so you have to drive active low or play other tricks. Some
later versions of the 8051 are quite nice hardware-wise (and I like
the programming model) but the original is a nasty bit of hardware,
IMHO. 


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 Spehro,

>>Somehow AD always comes to the rescue. My only gripe with this kind of 
>>stuff is the price, more than $2 for the ADM805. That would be about the 
>>same as the cost for a middle class uC.
>>    
>>
>
>We paid about 90 cents in 1K or 2K for it, IIRC. That was about 5-6
>years ago. Maxim never gave quotes that low, so maybe they got some
>design-ins and jacked the price up. 
>  
>
That could be although AD usually doesn't play that kind of game. The 
chip lists as non-stock at Digikey so maybe it isn't so popular anymore.

>>I'd still do it with a home grown reset and something like a 4060 for 
>>the WD timer. Until some company comes along with a chip that does it 
>>reliably for about 40 cents or so including any peripheral discretes.
>>    
>>
>
>Yeah, it really depends what's required. It would be nice if the
>microcontroller on-chip peripherals were both present and good enough
>to depend on. If you're not running the chip flat-out speed-wise,
>modern MCUs have enough voltage range that a sloppy & cheap voltage
>detection circuit will be good enough.
>
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.

> The original pseudo-bidirectional 8051 ports are nasty anyway- reset the chip and they become outputs and source enough current to turn on an NPN darlington, so you have to drive active low or play other tricks. Some later versions of the 8051 are quite nice hardware-wise (and I like the programming model) but the original is a nasty bit of hardware, IMHO. 
>  
>
The 89C51 was a tad better but I remember the drill, boot it and the 
first thing to do is set the ports right. We tried our best to avoid 
connecting anything that could smoke out if it would hang for some 
reason. It did have a very nice sleep mode feature though from which you 
could wake it up by wiggling the RS232 port. I guess the MSP series 
leads here these days since you can keep the realtime clock running, 
something we could not do with the C51 in the uA range.

Regards, Joerg

http://www.analogconsultants.com