Roman,

The SPI FRAM can be accessed using just a couple instructions per byte using
the hardware SPI. One trick you can use is not to bother checking for the
'completed' flag. You will "know" it has been set after the appropriate
number of instructions.

By setting the SPI clock to Tinst, you can 'pipelne' access to the FRAM at 9
(maybe 8) instructions per byte. While one byte is transfering you are
getting the next byte ready to send (on writes) or processing the previously
read byte (on reads).

Bob Ammerman
RAm Systems


----- Original Message -----
From: "Roman Black" <fastvid@EZY.NET.AU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, July 08, 2002 3:30 AM
Subject: Re: [PIC]: Cheap easy small ram


> Thanks Spehro, (and George too) for the suggestions.
> I really didn't want to use serial memory as the processor
> is very busy doing stuff and I can only spare a few
> instructions to read or write a whole byte. I think I
> have found a solution with a nifty circular buffer
> using the PICs internal ram, so I may not need the
> external memory after all. I think almost any product
> can be made with one PIC and one transistor... ;o)
> -Roman
>
>
> Spehro Pefhany wrote:
> >
> > At 10:44 PM 7/5/02 +1000, you wrote:
> > >I'm working on an idea for a robot navigation
> > >system using a PIC, but I need approx 2000 bytes
> > >or RAM. The ram only needs to be written/read
> > >sequentially,
>
> > How about using an SPI addressed FRAM? You'll get
> > really fast access and the newer ones have quite long
> > read/write life (but work it out). SPI access with
> > sequential read is *very* fast, limited mostly
> > by the maximum clock on the SPI port. Some can work
> > at 20MHz.
> >
> > Here is one:
> > http://www.ramtron.com/products/datasheets/FM25C160datasheet.pdf
> > (5 MHz 2K bytes, 10^10 read/writes life)
> >
> > This 8K x 8 one has unlimited read/writes and operates at 20MHz,
> > but only at 3V power:
> > http://www.ramtron.com/products/datasheets/FM25CL64ds_r0.3.pdf
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

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