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'[PIC]: Table write speed (FLASH) on 18F?'
2003\07\28@060804 by Alan B. Pearce

face picon face
> What is the approximate time it takes to table write a byte to program
> memory on the 18Fs? My requirements would be writing 8K of data (max) in
> <100 ms.
>
> Cheers,
> Ishaan

I would be very tempted to do this into an external I2C chip using one of
the FRAM family, as they are not speed limited on write.

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2003\07\28@061608 by

picon face
Alan B. Pearce wrote:

> I would be very tempted to do this into an external I2C chip using one of
> the FRAM family, as they are not speed limited on write.

Hm, there *is* a speed limit on both read an write. Now, in most
cases this will not be a limit for your PIC application, but you
might have to take care if running a 18F in 40Mhz...

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2003\07\28@070114 by Alan B. Pearce

face picon face
>Hm, there *is* a speed limit on both read an write. Now, in most
>cases this will not be a limit for your PIC application, but you
>might have to take care if running a 18F in 40Mhz...

Yeah, but the FRAM will work at full 400kHz I2C bus speed AFAIK, which has
nothing to do with the PIC speed when you calculate the divisor properly.

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2003\07\28@071421 by Spehro Pefhany

picon face
At 11:08 AM 7/28/2003 +0100, you wrote:
> > What is the approximate time it takes to table write a byte to program
> > memory on the 18Fs? My requirements would be writing 8K of data (max) in
> > <100 ms.
> >
> > Cheers,
> > Ishaan
>
>I would be very tempted to do this into an external I2C chip using one of
>the FRAM family, as they are not speed limited on write.

There are SPI versions of the FRAM chips. For example, the FM25640 is
8K x 8 and can operate at a 5MHz bus frequency.

It also supports sequential write mode (which I don't normally like
much, but might be just the ticket here). All you need to do is set it up,
then pump the bytes sequentially into the SPI register on any PIC with
hardware SPI- less than 2usec per byte, much faster than the application
requires, and only a few port pins consumed.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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2003\07\28@073401 by Ishaan Dalal
flavicon
face
> There are SPI versions of the FRAM chips. For example, the FM25640 is
> 8K x 8 and can operate at a 5MHz bus frequency.

   Those might just be the ticket. The data is wavetable/lookup values, so
sequential write is even better.

Cheers,
Ishaan

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