Need some help with the LPC901 and data flash storage.  I'm using pin
7 as s digital input to determine when power is going to be lost.  The
hardware is setup such that pin 7 drops to a low level well before the
chip itself powers down.  When I see a 0 at pin 7 I write a counter
value to flash at 0x02.  The problem is that when I power the chip
back up and read the counter value from flash sometimes the value
seems to be fine other times it acts like the value being read is 0. 
I've tried simulating power down on pin 7 while maintaining power to
the chip and this seems to work ok.  Is something going on during
power up of the chip that's causing the value that I have written to
flash to change.  Would appreciate any input on this.
	

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--- In lpc900_users@lpc9..., "lgunseor" <lgunseor@...> wrote:
> When I see a 0 at pin 7 I write a counter
> value to flash at 0x02.  The problem is that when I power the chip
> back up and read the counter value from flash sometimes the value
> seems to be fine other times it acts like the value being read is 0. 
>

Hi there,
I doubt that the location is being corrupted as power is reapplied. If 
this were possible then there is a greater chance of a valid program 
location being corrupted by the same mechanism than your written 
location.

Some things to check:
 - that the signal on pin 7 is clean

 - the erase and program operation take 4ms and must be complete before 
you loose power (taking into account the worst case latency for testing 
pin 7). If the brownout detector fires before this is complete you may 
find the value is FFh or 00h depending on where in the erase cycle the 
abort occurred.

If you are concerned about the integrity of the number stored then you 
could store it's compliment in the byte next door (pick an unused 
interrupt vector for 8-bytes of consecutive storage), or use some 
checksum scheme.

I presume you are using the recommended erase/program command (as this 
preserves unaltered bytes in the page)?

Regards,
Phoebe
	

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Phoebe,

Thanks for the feedback.  I'm using the "C" program examples provided in the
LPC901/902/903 Users Manual for reading and writing to flash.  I wish you could download
the contents of the flash memory to see what values have been stored but you can't do that
on the LPC900 series.  I'm using the RTC to provide a 1 second cycle time through the RTC
interrupt routinue.  This provides my 1 second counter.  I write the counter value to
Flash if the voltage on pin 7 drops to a zero.  I make sure that I globally disable all
interrupts before writing or reading flash.  For testing purposes I set a limit that when
reached by the counter is written to the flash and turns on an LED.  I disable the RTC and
all interrupts at this point.  When I power the system down and back up again the first
thing I do is read the flash, compare it to the limit value (they should be the same if
the flash value hasn't changed) and turn on the LED.  When I power the system off and on
sometime the LED light
s telling me the value is the same and sometimes it doesn't meaning something has
changed.

Regards,
Larry

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