Memory question

Archiver

In my application, I would like to be able to store data taken in a
certain time period, and then download that data to my PC at some
future time.

At a minimum, I would like to store at least 50,000 Words (100kbytes).
In theory, I could come up with a more efficient scheme (including
compression?), but that is the order of magnitude.

Forgive my ignorance on this subject ... how easy is it to interface a
RAM chip of this size to the BS2? I've seen the AppNote on the 8k
EEPROM; is it that simple for a larger RAM chip? Are there larger
EEPROM chips? I'd rather use RAM than EEPROM, as I will be writing and
reading often (once per day ...). Power loss is no concern.

If this is possible, please provide suggestions on which RAM chip(s)
to use, and how to do it in software/hardware (unless it's as easy as
the EEPROM).

Michael

Archiver

1. EEPROM: 24C640 is an 8K x 8 bit EEPROM,
SPI interfaced -- uses SHIFTOUT to write.
8-pin chip.

2. 6864 is an 8K x 8 SRAM -- parallel interfaced,
so it takes quite a few pins to write/read.

3. There are 32 KByte, and 512 KByte SRAMS.
See Jameco's catelog.

4. There also exist SRAMS which have built-in
batteries. See www.digikey.com.



--- In basicstamps@yahoogroups.com, "webbm03" <webbm@c...> wrote:
> In my application, I would like to be able to store data taken in a
> certain time period, and then download that data to my PC at some
> future time.
>
> At a minimum, I would like to store at least 50,000 Words
(100kbytes).
> In theory, I could come up with a more efficient scheme (including
> compression?), but that is the order of magnitude.
>
> Forgive my ignorance on this subject ... how easy is it to
interface a
> RAM chip of this size to the BS2? I've seen the AppNote on the 8k
> EEPROM; is it that simple for a larger RAM chip? Are there larger
> EEPROM chips? I'd rather use RAM than EEPROM, as I will be writing
and
> reading often (once per day ...). Power loss is no concern.
>
> If this is possible, please provide suggestions on which RAM chip(s)
> to use, and how to do it in software/hardware (unless it's as easy
as
> the EEPROM).
>
> Michael

Archiver

You can't use a typical RAM chip by itself, Michael. They require controller
IC's of their own to keep the data refreshed. Statics don't, but that's a
different class of problem. Several storage chip categories are intended for
the sort of use you have in mind, but EEPROM's are probably the easiest for
you to interface.

You need a serial interface of some sort because the address for a large
memory space would use up all the I/O pins on your stamp. And then some: 32
kilobytes takes 15 bits of address, and 8 more for the data lines. Unless
you want to design your own serial interface, you want a storage chip with a
built-in serial interface. I haven't looked recently, but I can't imagine
why any designer would provide that with a RAM chip. EEPROM chips with a
serial interface are available up to 1 megabit, though I don't know of a
source for 1 megabit parts in quantity one. Of course, with most serial
interfaces, stringing several of them to get very large storage spaces is
not difficult.

As an example, the Microchip 24LC515 provides 512 kbits (64 kbytes) of
storage, supports the I2C serial interface, allows four units to be
configured together, saves the data for more than 200 years, and permits
100,000 erase/write cycles.

See http://makeashorterlink.com/?P2DC12A46 for the spec. Digikey wants less
than $5 apiece for these in quantity one. And you probably don't really need
that much capacity. I just went to the largest EEPROM I could find listed at
Digikey with quantity one pricing.

> I'd rather use RAM than EEPROM, as I will be writing and
> reading often (once per day ...).

As to that last consideration, you really are not writing very often, and
the limit is based on the most difficult conditions the chip is designed to
endure. For example, operating temperatures of 85 C and high charge pump
voltages while writing. Even at that, it would take your once-a-day write
cycle 274 years to reach the design limit.

If you're seriously concerned about this aspect, check app note 601 at
Microchip http://makeashorterlink.com/?X28D15A46 which provides an
explanation of endurance issues in EEPROM chips.

Gary

Archiver

>In my application, I would like to be able to store data taken in a
>certain time period, and then download that data to my PC at some
>future time.
>
>At a minimum, I would like to store at least 50,000 Words (100kbytes).
>In theory, I could come up with a more efficient scheme (including
>compression?), but that is the order of magnitude.
>
>Forgive my ignorance on this subject ... how easy is it to interface a
>RAM chip of this size to the BS2? I've seen the AppNote on the 8k
>EEPROM; is it that simple for a larger RAM chip? Are there larger
>EEPROM chips? I'd rather use RAM than EEPROM, as I will be writing and
>reading often (once per day ...). Power loss is no concern.
>
>If this is possible, please provide suggestions on which RAM chip(s)
>to use, and how to do it in software/hardware (unless it's as easy as
>the EEPROM).
>
>Michael

Hi Micheal,

Once per day does not usually qualify as "often"! Flash & eeprom
devices are good for 100s of thousands of rewrites. Once per second
per memory location, that is another matter.

The Atmel AT45DB041 is 512k bytes of flash+RAM in an 8 pin wide SOIC.
One complication is that the AT45 parts Atmel is currently shipping
operate only at 2.7 to 3.6 volts. The command set is formidable (or
powerful, depending on your point of view), but otherwise it is quite
easy to interface to the Stamp. I have a description posted at
http://www.emesystems.com/BS2flash.htm,

(I have a board available that combines that chip and the necessary
interface with a BS2pe--contact me off list if you'd like more
information about that.)

-- -- regards,
Tracy Allen
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com