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'[PIC]: Cheap easy small ram'
2002\07\05@084620 by Roman Black

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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, but I need decent speed and don't
have that many PIC pins.

I can spare 8 pins for the data port (read/write)
and a clock and reset pin, and read/write pin, is
11 pins total. Maybe 12 pins available if necessary.

I don't want to use flash eeprom or any I2C addressed
memory as it is constantly reading/writing at a fair
speed. ie must be parallel data read/write.

Any suggestions for a cheap, minimum chip solution
to get the extra 2000 or 4000 bytes of RAM attached
to my PIC?
:o)
-Roman

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2002\07\05@090319 by Spehro Pefhany

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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, but I need decent speed and don't
>have that many PIC pins.
>
>I can spare 8 pins for the data port (read/write)
>and a clock and reset pin, and read/write pin, is
>11 pins total. Maybe 12 pins available if necessary.
>
>I don't want to use flash eeprom or any I2C addressed
>memory as it is constantly reading/writing at a fair
>speed. ie must be parallel data read/write.

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:
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


Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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2002\07\05@094029 by Geo

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On 5 Jul 2002, at 22:44, Roman Black 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, but I need decent speed and don't
> have that many PIC pins.
>
> I can spare 8 pins for the data port (read/write)
> and a clock and reset pin, and read/write pin, is
> 11 pins total. Maybe 12 pins available if necessary.
>
> I don't want to use flash eeprom or any I2C addressed
> memory as it is constantly reading/writing at a fair
> speed. ie must be parallel data read/write.
>
> Any suggestions for a cheap, minimum chip solution
> to get the extra 2000 or 4000 bytes of RAM attached
> to my PIC?
I normally use a 4040 (or 74xxx equiv) counter to supply the address
lines.
This just needs reset and clock.
R/W pin from uP direct to RAM.

regards,
George Smith

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2002\07\07@102138 by Greg Oxelis

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At what rate do you access the memory?
I have a system using serial eeproms where I buffer the data, interleave
between devices, use the devices page mode, and checks to see if the
previous write is done. The system is not fully tested yet, but is designed
to allow data to be stored at several or even 10s of K bytes per second.
Very few parts/pins are needed.

I'm sampling pressure and thrust data for a few seconds at 1000 samples per
second. I will provide more info if you are interested.

Greg
{Original Message removed}

2002\07\08@033225 by Roman Black

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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:
{Quote hidden}

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2002\07\08@033437 by Roman Black

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Greg Oxelis wrote:
>
> At what rate do you access the memory?
> I have a system using serial eeproms where I buffer the data, interleave
> between devices, use the devices page mode, and checks to see if the
> previous write is done. The system is not fully tested yet, but is designed
> to allow data to be stored at several or even 10s of K bytes per second.
> Very few parts/pins are needed.
>
> I'm sampling pressure and thrust data for a few seconds at 1000 samples per
> second. I will provide more info if you are interested.


Hi Greg, thanks for the help but serial eeproms really
aren't fast enough for this app, mainly because I need
the processor for other stuff at the time.
But I am interested in your water rocket (guessing!!?)
;o)
-Roman

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2002\07\08@075616 by Bob Ammerman

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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 removed}

2002\07\08@193133 by Roman Black

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Thanks Bob, actually I didn't think of using the
hardware SPI. :o)
-Roman


Bob Ammerman wrote:
{Quote hidden}

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2002\07\08@200020 by Bob Ammerman
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Btw: The reason I say 9 (maybe 8) instructions below is because my
experiments with the SPI module indicated that it can not do back-to-back
operations every eight cycles as one would hope it could (and should?) do.

Bob Ammerman
RAm Systems

{Original Message removed}

2002\07\09@155045 by Peter L. Peres

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On Fri, 5 Jul 2002, Spehro Pefhany wrote:

>Here is one:
>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

Are these on sale somewhere in smally qty? Like Digi-key, Mouser, etc ?

thanks,

Peter

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