Hi ALL,

I have a simple question.
I read P89LPC935 errata sheet.
The following is written in it.

"To generate a proper Power-On-Reset(POR), VDD must have dropped below
0.2V before being powered back up.Power-cycling without VDD having
dropped below 0.2V may result in incorrect Program Counter values. "

BrownOut reset operates when falling into Vdd=2.7V.
When Brown out reset happens and vdd is restored from 0.2~2.4V(
Power-on reset doesn't happen), is the program counter correctly
cleared?

Please teach when someone knows!



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Hi there,
> "To generate a proper Power-On-Reset(POR), VDD must have dropped
below
> 0.2V before being powered back up.Power-cycling without VDD having
> dropped below 0.2V may result in incorrect Program Counter values. "

This is true - a clean POR requires Vdd to have dropped below 0.2V.

> BrownOut reset operates when falling into Vdd=2.7V.
> When Brown out reset happens and vdd is restored from 0.2~2.4V(
> Power-on reset doesn't happen), is the program counter correctly
> cleared?

The device is specified to operate from 2.4V to 3.6V, while the
BrownOut detector will activate between 2.4V and 2.7V. This means
that the BrownOut detector triggers while the device is still
correctly operating.

The 'primary' (IMHO) use of the BrownOut detector is to warn (by
ineterrupt or flag) the device that power is becoming critical so
that the application can take appropriate action.

The 'secondary' (IMHO) use is to freeze (by reset) the device until
the power is restored. This is fine as long as the Vdd doesn't dip
too far (i.e. below 2.4V) in which case you may need to provide an
external reset rather than relying on the internal one. I think that
below 2.4V a complete POR is expected, with constraints on risetimes,
etc, to ensure a clean start.

A worst case scenario would probably be a device running directly off
batteries so that they can drift below 2.4V and slowly rise again as
their charge is restored. In that case I would certainly emply some
form of external reset generator.

PM



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Dear PM

Thank you for your advice.
if so I want to know way to restore from 0.2V~2.4V.

In the circuit that suppresses current consumption small as much as
possible, to drop the power-supply voltage to 0.2V, time is
considerably required.
Electricity is not discharged from especially 0.6V easily.
When greatly waiting, it can meet the requirement of PowerON reset.

If power supply is restored without falling down to 0.2V,
Is it possible to ensure recovery by external reset?
Is there other technique?

--- In l...@yahoogroups.com, "phb_miller"
wrote:
>
> Hi there,
> > "To generate a proper Power-On-Reset(POR), VDD must have dropped
> below
> > 0.2V before being powered back up.Power-cycling without VDD
having
> > dropped below 0.2V may result in incorrect Program Counter
values. "
>
> This is true - a clean POR requires Vdd to have dropped below 0.2V.
>
> > BrownOut reset operates when falling into Vdd=2.7V.
> > When Brown out reset happens and vdd is restored from 0.2~2.4V(
> > Power-on reset doesn't happen), is the program counter correctly
> > cleared?
>
> The device is specified to operate from 2.4V to 3.6V, while the
> BrownOut detector will activate between 2.4V and 2.7V. This means
> that the BrownOut detector triggers while the device is still
> correctly operating.
>
> The 'primary' (IMHO) use of the BrownOut detector is to warn (by
> ineterrupt or flag) the device that power is becoming critical so
> that the application can take appropriate action.
>
> The 'secondary' (IMHO) use is to freeze (by reset) the device
until
> the power is restored. This is fine as long as the Vdd doesn't dip
> too far (i.e. below 2.4V) in which case you may need to provide an
> external reset rather than relying on the internal one. I think
that
> below 2.4V a complete POR is expected, with constraints on
risetimes,
> etc, to ensure a clean start.
>
> A worst case scenario would probably be a device running directly
off
> batteries so that they can drift below 2.4V and slowly rise again
as
> their charge is restored. In that case I would certainly emply
some
> form of external reset generator.
>
> PM
>



(You need to be a member of LPC900_users -- send a blank email to LPC900_users-subscribe@yahoogroups.com )

Hi there,

> If power supply is restored without falling down to 0.2V,
> Is it possible to ensure recovery by external reset?
> Is there other technique?

The IAP code is protected by a software reset instruction so that a
processor walking up through unused code memory will be correctly
reset, and thereby minimise the likelyhood that it will alter the code
memory.

You may be able to do something similar and force a software reset.

> In the circuit that suppresses current consumption small as much as
> possible, to drop the power-supply voltage to 0.2V, time is
> considerably required.
> Electricity is not discharged from especially 0.6V easily.
> When greatly waiting, it can meet the requirement of PowerON reset.

The 'real' solution is to design your supply circuit such that if the
supply voltage falls below 2.4V that the external reset is applied.
This solves the problem by ensuring that the chip is correctly
restarted once the supply recovers. I agree that getting the supply
right down to 0.2V can be a challenge without drawing unnecessarily
large current, so a simple resistor is unlikely to do the trick for you.

IMHO the necessity to reach 0.2V is to ensure that the internal reset
correctly recovers the device. Maybe the proper application of a
external reset under the conditions you facing would be good protection?

PM



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