Lpc2000

Dear Friends,

I am trying to make an evaluation board for myself and later for 
commercial purpose based on LPC2106. I have little doubts on reset 
circuitry. I am planning to use a RC circuit of 10K and 100nF to 
reduce the cost. Otherwise is it compulsory to use Reset IC for this 
purpose. Please suggest me on this circuit.

Thanks in advance.

Regards,

Rajneesh Raju

----- Original Message ----- 

From: "vrrraju" <vrrraju@...>
To: <lpc2000@yahoogroups.com>
Sent: Saturday, February 28, 2004 4:44 AM
Subject: [lpc2000] Reset Circuit


> Dear Friends,
> 
> I am trying to make an evaluation board for myself and later for 
> commercial purpose based on LPC2106. I have little doubts on reset 
> circuitry. I am planning to use a RC circuit of 10K and 100nF to 
> reduce the cost. Otherwise is it compulsory to use Reset IC for this 
> purpose. Please suggest me on this circuit.

That's what I used.

Leon

--- In lpc2000@yahoogroups.com, "vrrraju" <vrrraju@y...> wrote:
> Dear Friends,
> 
> I am trying to make an evaluation board for myself and later for 
> commercial purpose based on LPC2106. I have little doubts on reset 
> circuitry. I am planning to use a RC circuit of 10K and 100nF to 
> reduce the cost. Otherwise is it compulsory to use Reset IC for this 
> purpose. Please suggest me on this circuit.
> 
> Thanks in advance.

This is a tricky circuit depending on how well you want it to work. 
Most modern MCUs have a POR (power on reset) and BOD (brown out
detect) built in.  I am surprised that the LPC parts don't.  

If you are just doing a hobbiest design, an RC will work ok.  But if
you plan to sell this board commercially, you will want to use a POR
chip.  The problem with an RC circuit is that although it works great
for power up, it does not work for power down or for any short
duration or brown out power conditions.  If the voltage drop is
shorter than your RC time, the chip will not be reset, but can be
upset.  If the voltage does not go to ground, same thing.  

If you are adding your own power regulators, you can often find units
that have a power ok output.  These can normally be wire OR'd together
to control the reset.  Some even provide a timeout period.  

If you want reliable reset operation, use an external chip.  And
complain to Philips.  There is no reason that they could not have
added POR and BOD to their devices.

At 04:40 PM 2/28/04 +0000, you wrote:
>--- In lpc2000@yahoogroups.com, "vrrraju" <vrrraju@y...> wrote:
> > Dear Friends,
> >
> > I am trying to make an evaluation board for myself and later for
> > commercial purpose based on LPC2106. I have little doubts on reset
> > circuitry. I am planning to use a RC circuit of 10K and 100nF to
> > reduce the cost. Otherwise is it compulsory to use Reset IC for this
> > purpose. Please suggest me on this circuit.
> >
> > Thanks in advance.
>
>This is a tricky circuit depending on how well you want it to work.
>Most modern MCUs have a POR (power on reset) and BOD (brown out
>detect) built in.  I am surprised that the LPC parts don't.

I don't know about most.  The ones I've worked with in the past haven't.

I'd use a reset/supervisory circuit myself, they are inexpensive and small 
if you only monitor a single voltage.  I've not found an inexpensive 
multi-voltage monitor.  The closest I've found were some Maxim parts but 
they noted that they wanted minimum orders above 10K units.  You can get 
away with a single monitor if you monitor the voltage that is common to all 
of your voltages and are willing to take the chance that the lower voltages 
will be OK if the higher one is.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III

I'm using the TI TPS77733 for 3.3 volts and the TPS77118 for 1.8
volts.  Both have open-drain, delayed release, -RESET signals which I
tie together and pull-up with a 10K.  That signal is then connected to
the LPC -RESET input.  The 3.3v reg is a bit overkill but is also
powering a bunch of other stuff on the board.  Both are pretty
inexpensive and available from DigiKey.

-Bill Knight
R O SoftWare



On Sat, 28 Feb 2004 17:39:54 -0500, Robert Adsett wrote:

At 04:40 PM 2/28/04 +0000, you wrote:
>--- In lpc2000@yahoogroups.com, "vrrraju" <vrrraju@y...> wrote:
> > Dear Friends,
> >
> > I am trying to make an evaluation board for myself and later for
> > commercial purpose based on LPC2106. I have little doubts on reset
> > circuitry. I am planning to use a RC circuit of 10K and 100nF to
> > reduce the cost. Otherwise is it compulsory to use Reset IC for this
> > purpose. Please suggest me on this circuit.
> >
> > Thanks in advance.

>This is a tricky circuit depending on how well you want it to work.
>Most modern MCUs have a POR (power on reset) and BOD (brown out
>detect) built in.  I am surprised that the LPC parts don't.

I don't know about most.  The ones I've worked with in the past haven't.

I'd use a reset/supervisory circuit myself, they are inexpensive and small 
if you only monitor a single voltage.  I've not found an inexpensive 
multi-voltage monitor.  The closest I've found were some Maxim parts but 
they noted that they wanted minimum orders above 10K units.  You can get 
away with a single monitor if you monitor the voltage that is common to all 
of your voltages and are willing to take the chance that the lower voltages 
will be OK if the higher one is.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III





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Bill Knight wrote:
> I'm using the TI TPS77733 for 3.3 volts and the TPS77118 for 1.8
> volts.  Both have open-drain, delayed release, -RESET signals which I
> tie together and pull-up with a 10K.  That signal is then connected to
> the LPC -RESET input.  The 3.3v reg is a bit overkill but is also
> powering a bunch of other stuff on the board.  Both are pretty
> inexpensive and available from DigiKey.

I'm putting a Maxim uP supervisory reset generator chip in mine, on the 
3.3v line, with a reset threshold of 3.1v - I'm hoping that'll do for now.

> 
> -Bill Knight
> R O SoftWare
> 

ABS