need data stored when power if off - EEPROM or RAM ?
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--- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> >Hi there... I need a process where I can store a 4 digit number
> >somehow, generated from the BS2 to be brought back when BS2 is back
> >on. In other words I need a way to keep track of a counter so BS2
can
> >read the old count and then add to that when turned back on.
Somehow
> >like a clock, that has also the ability to store a number (up to 4
> >digits).
> >PLEASE HELP..... Thank you all.
>
> Many real time clock chips include additional RAM that is perfect
for
> this purpose. The real time clock and its RAM are backed up by a
> battery or a capacitor.
>
> On the Stamp itself, you can store the counter in EEPROM if it only
> has to be done occasionally. Each location in the EEPROM has a
> limited life for write cycles, somewhere in the 10000 to 100000
> range. At once a day, no problem, but at once a second, well,
there
> are 86400 seconds in a day.
We ran into this problem. the typical EEPROM has a write cycle of
around 100,000 or so. For the Stamp program, I don't think any of
us could write 100,000 programs to a stamp. 10 writes a day, every
day is over 3 years non-stop.
But, for data logging, you can hit that pretty fast. Not that you
would, as you would typically write a whole page, then store that so
the individual point write is not the same as chip writes.
The problem comes in from the charge on writing. The EEPROM has an
internal charge pump and writes at around 14 volts. That zaps the
memory cell at tiny bit each time and after so many writes, the cell
is gone.
But, as you pointed out RAM offers almost the exact same ability to
access the chip memory, but because of the lower charge for writing
to a memory location. a RAM chip uses something on the order of 3
volts and therefore does not 'chew up' memory.
Unfortunately RAM memory chips are more expensive and not as large.
Typically one can get a 1024 EEPROM, but only a 256 RAM chip.
The RAM chip being about 5 times the cost.
If I can read into the poster's notes, it seems he is looking for
when the Stamp powers up, so I would expect that to be a daily or
hourly occurrence. And for that, an EEPROM will probably offer years
of service life. Figure once per hour and you get over 10 years on
an EEPROM.
and, the reason I know this is (shameless plug) we added EEPROM to
the ChipCircuit line and offer a RAM option by request as we get the
software tested.
Dave
New item – CC-EEPOM … and New prices.........
http://www.visualmuses.com/chipcircuit/index.html
We have EEPROM AND RAM options.
New item - New prices.........
http://www.visualmuses.com/chipcircuit/index.html
> >Hi there... I need a process where I can store a 4 digit number
> >somehow, generated from the BS2 to be brought back when BS2 is back
> >on. In other words I need a way to keep track of a counter so BS2
can
> >read the old count and then add to that when turned back on.
Somehow
> >like a clock, that has also the ability to store a number (up to 4
> >digits).
> >PLEASE HELP..... Thank you all.
>
> Many real time clock chips include additional RAM that is perfect
for
> this purpose. The real time clock and its RAM are backed up by a
> battery or a capacitor.
>
> On the Stamp itself, you can store the counter in EEPROM if it only
> has to be done occasionally. Each location in the EEPROM has a
> limited life for write cycles, somewhere in the 10000 to 100000
> range. At once a day, no problem, but at once a second, well,
there
> are 86400 seconds in a day.
We ran into this problem. the typical EEPROM has a write cycle of
around 100,000 or so. For the Stamp program, I don't think any of
us could write 100,000 programs to a stamp. 10 writes a day, every
day is over 3 years non-stop.
But, for data logging, you can hit that pretty fast. Not that you
would, as you would typically write a whole page, then store that so
the individual point write is not the same as chip writes.
The problem comes in from the charge on writing. The EEPROM has an
internal charge pump and writes at around 14 volts. That zaps the
memory cell at tiny bit each time and after so many writes, the cell
is gone.
But, as you pointed out RAM offers almost the exact same ability to
access the chip memory, but because of the lower charge for writing
to a memory location. a RAM chip uses something on the order of 3
volts and therefore does not 'chew up' memory.
Unfortunately RAM memory chips are more expensive and not as large.
Typically one can get a 1024 EEPROM, but only a 256 RAM chip.
The RAM chip being about 5 times the cost.
If I can read into the poster's notes, it seems he is looking for
when the Stamp powers up, so I would expect that to be a daily or
hourly occurrence. And for that, an EEPROM will probably offer years
of service life. Figure once per hour and you get over 10 years on
an EEPROM.
and, the reason I know this is (shameless plug) we added EEPROM to
the ChipCircuit line and offer a RAM option by request as we get the
software tested.
Dave
New item – CC-EEPOM … and New prices.........
http://www.visualmuses.com/chipcircuit/index.html
We have EEPROM AND RAM options.
New item - New prices.........
http://www.visualmuses.com/chipcircuit/index.html