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'Looking for an easy ram buffer...'
1998\04\01@165929 by SHAWN ELLIS

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Hi all,

I have a project in which I am looking to save about 1 or 2 MB of
data from an A/D in a RAM buffer.

Can anyone recommend an easy to use RAM buffer?  Money is no object
but it must:

1.  Be at least 1 or 2 MB.

2.  Use an 8 or 16 bit parrallel bus (I may be flexable on that.)

3.  Be exceptionally easy to set up and interface to...  No manual
refreshing!

Other than that, anything will do!

Thanks,

1998\04\01@174338 by John Mellert

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Do you really need random access?

I believe IDT makes a range of FIFOs (first in first out) memories.
Essentially you strobe a WRITE pin to sequentially store data and strobe a
READ pin to retrieve the data which saves you the hassle of handling
addressing.

John Mellert
EVI Inc.
Columbia, MD

spam_OUTjmellertNOTakeThisOuTspamSPAMevi-inc.com


SHAWN ELLIS wrote:


snip
{Quote hidden}

snip

1998\04\02@024321 by Michael Ghormley

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SHAWN ELLIS wrote:

> Can anyone recommend an easy to use RAM buffer?  Money is no object
> but it must:

> 1.  Be at least 1 or 2 MB.

> 2.  Use an 8 or 16 bit parrallel bus (I may be flexable on that.)

> 3.  Be exceptionally easy to set up and interface to...  No manual
refreshing!

Maybe I'm missing something, but it sounds like you want a big SRAM chip.

There is a Toshiba 512Kx8 SRAM at Digi-Key (Part# TC554001FL-70-ND) for $35 and
some change.  It matches your requirements.  Two of `em would give you a meg and
four would give you...

But if you don't need random access you might think about a FIFO instead.

Just my opinion -- YMMV.

Michael

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1998\04\02@081454 by Tom Handley

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  Shawn, other's have mentioned FIFOs but they are very expensive and very
limited in size if you want to store 1-2MB. Industry-standard 512K x 8 SRAM
costs around $20 (~70ns) in single quantity.

  The nice thing about FIFOs is that they are very easy to interface to with
little or no `glue' logic. I looked at FIFOs from several vendors when I was
researching my logic analyzer. IDT seems to be a clear winner as far as price
and capacity. You mentioned "money was no object". In that case they have
devices up to 128K. Again, they are `extremely' expensive...

  If you go with 512K x 8 SRAMs, you will need to generate a 20-21 Bit
address and provide 2-4 chip-selects. You can easily do this in a simple CPLD
or 74x family `glue' logic.

  - Tom

At 04:58 PM 4/1/98 EST5EDT, you wrote:
{Quote hidden}

1998\04\02@105024 by SHAWN ELLIS

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> SHAWN ELLIS wrote:
>
> > Can anyone recommend an easy to use RAM buffer?  Money is no object
> > but it must:
>
> > 1.  Be at least 1 or 2 MB.
>
> > 2.  Use an 8 or 16 bit parrallel bus (I may be flexable on that.)
>
> > 3.  Be exceptionally easy to set up and interface to...  No manual
>  refreshing!
>
> Maybe I'm missing something, but it sounds like you want a big SRAM chip.
>
> There is a Toshiba 512Kx8 SRAM at Digi-Key (Part# TC554001FL-70-ND) for $35
and
> some change.  It matches your requirements.  Two of `em would give you a meg
and
> four would give you...
>
> But if you don't need random access you might think about a FIFO instead.
>
> Just my opinion -- YMMV.
>
> Michael
>
Yeah, I don't need random access, so I guess a FIFO would do...  Any
sugestions as to where I could look for one of those?

thanks,

1998\04\02@123737 by Michael Hagberg

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there is also in http://www.digikey.com a ADM flash memory 1MB x 8 for $21.50
remember if you don't have the i/o to connect to this device you could use a
pic to control the memory and program it as a 2 wire serial eeprom format.

michael


{Original Message removed}

1998\04\02@133551 by Jon Baker

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>
>Yeah, I don't need random access, so I guess a FIFO would do...  Any
>sugestions as to where I could look for one of those?
>
>thanks,

AMD make some fairly cheap fifos. Not sure if they go up to 1 or 2 meg
though, you can always daisy-chain them together though, usefull for adding
more memory on later.

1998\04\02@161657 by Jerry Meng

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At 11:37 AM 4/2/98 -0600, you wrote:
>there is also in http://www.digikey.com a ADM flash memory 1MB x 8 for $21.50
>remember if you don't have the i/o to connect to this device you could use a
>pic to control the memory and program it as a 2 wire serial eeprom format.
If you prefer Flash memory, why don't you try the ATMEL data flash, there
are 1MB x 8, 512KB x 8 and 256KB x 8 for your choice, data flash use SPI
interface, compatible with Motorola, ATMEL and PIC MCUs, the price is
about $10 for more than 1,000 pieces.



Jerry Meng, BA1FB

.....ba1fbKILLspamspam@spam@qsl.net
http://www.qsl.net/ba1fb

1998\04\02@171016 by SHAWN ELLIS

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These have all been very interesting suggestyions...  Here are my
problems so far:

FIFOs are too small.  Even stringing them together is to complicated.

DRAM's and SRAM's take too many I/O lines...  Mabye I should
use an IIC RAM?  Does anyone know of an IIC RAM that Large?  (1 - 2
MB)

The suggestion to use another PIC is a good one, but I hate to add
THAT much complexity to the system.  Especially since there SHOULD be
a RAM module out there SOMEWHERE that does IIC or SPI.

FLASH RAM worries me because I don't need all the battery-backup
mess, I'm not sure if it's fast enough, and I don't want to add even
more complexity if I can get away with just a RAM chip...

So, keep those suggestions coming, the search goes on...

Thanks,

1998\04\02@212923 by Mike Keitz

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On Thu, 2 Apr 1998 17:09:34 EST5EDT SHAWN ELLIS <spespamKILLspamMERC.RX.UGA.EDU>
writes:
>These have all been very interesting suggestyions...  Here are my
>problems so far:

Most people are taking stabs in the dark with their answers because you
haven't provided enough information about the application.  We need to
know things like:

How fast does the data need to be written and read?  Is it ever read?
(If not, there's no need to store it...).  How often is the data
re-written?  Is the use mostly to write once then read very rapidly, or
is it read and written rapidly?

Does the data need to be saved while the power is off?  How much power
can the RAM sub-system use while the power is on?

Are there any limits on physical space and weight?

>
>FIFOs are too small.  Even stringing them together is to complicated.

Your definition of "complicated" (is this the only major concern?) is
apparently very restrictive.

>DRAM's and SRAM's take too many I/O lines...  Mabye I should
>use an IIC RAM?  Does anyone know of an IIC RAM that Large?  (1 - 2
>MB)
>The suggestion to use another PIC is a good one, but I hate to add
>THAT much complexity to the system.  Especially since there SHOULD be
>a RAM module out there SOMEWHERE that does IIC or SPI.

There are serial Flash ROMs (*) in this size.  I don't think there are
any RAMs with built in serial interface.  But, Dallas Semiconductor makes
adapter chips that can be connected to standard SRAMs or DRAMs to access
them through a serial interface and supply backup power from a battery.
Someone suggested using another PIC instead because the Dallas chips are
I think more expensive than PICs and may not do exactly what's needed.

>FLASH RAM worries me because I don't need all the battery-backup
>mess, I'm not sure if it's fast enough, and I don't want to add even
>more complexity if I can get away with just a RAM chip...

(*)  Flash ROM (it isn't called Flash RAM) can keep data permanently
without any power at all.  Batteries are required for SRAM or DRAM.
However, writing the data is somewhat slow and can only be done a limited
number of times before the chip literally "wears out".  Reading is, for
practical purposes, as fast as SRAM or DRAM and does not cause wearout.
These limitations may not be a problem with your application because the
current technology allows a couple hundred K per second to be written and
several million writes before wearout.

I think Andrew Warren or one of the other old-timers has prepared a
useful table comparing the different memory technologies.

>So, keep those suggestions coming, the search goes on...

Based on your original requirements (cost not at all a problem,
complexity a very big problem, anything else goes) I'd suggest using a PC
with about 4 MB of RAM installed.  Then it's just a matter of a couple of
lines of C code to set up and use a 2 MB buffer.

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1998\04\02@234916 by tjaart

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SHAWN ELLIS wrote:

> These have all been very interesting suggestyions...  Here are my
> problems so far:
>
> FIFOs are too small.  Even stringing them together is to complicated.
>
> DRAM's and SRAM's take too many I/O lines...  Mabye I should
> use an IIC RAM?  Does anyone know of an IIC RAM that Large?  (1 - 2
> MB)

http://www.idt.com makes a 4Mb fifo. I think it will rattle your wallet a bit though....

--
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1998\04\03@122515 by SHAWN ELLIS

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> How fast does the data need to be written and read?  Is it ever read?
> (If not, there's no need to store it...).  How often is the data
> re-written?  Is the use mostly to write once then read very rapidly, or
> is it read and written rapidly?
>
Ok, here it is:

It's a PIC1674 with an AD676 parrallel, 16-bit A/D attached.  It will
need to read about 60,000 samples from the A/D at 100 Hz.  I'd like
to be able to throw the samples into the RAM buffer in at most 1 ms.
Right now I'm running low on I/O lines, so I'd like the RAM to be
serial.  I'm also going to add another A/D to the system, meaning not
only will my timing requirements get tighter, but I'll need twice as
much RAM to store the data.  Anyway, the data will sit in the ram
until the host PC decides to get it by RS232 from the same PIC.

Given these problems, I think it is safe to say the following:

I don't need or want non-volitile storage because of
speed/complexity/endurance problems.

I need serial interfaceing becuase of the lack of I/O lines.

I need at LEAST 256 KB of RAM to store a potential 64,000 samples of
two 16-bit A/D's.

Any more questions, please ask...  I'd like to make a decision pretty
soon...

Thanks for the help!

1998\04\03@125229 by Alex Torres

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> From: SHAWN ELLIS <spespamspam_OUTMERC.RX.UGA.EDU>

If you are not need to save the information without a power you may use a
DRAM.
There WAS wonderful chip from National Semicondactor - NM29A080 - 8mbit
flash memory with MICROWIRE serial interface, but unfortunately this chip
is not availiable now :-((

In one of my designes I use Intel 28F008SA Flash with PIC16C74 and cmos
counters as addresses (becouse I don't need random access).

Alex Torres, Kharkov, Ukraine (exUSSR)
@spam@altorKILLspamspamchat.ru
2:461/28 FidoNet
www.geocities.com/SiliconValley/Lab/6311

1998\04\03@130805 by Christoph Klein

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Shawn,

right now I am facing the same question. I am leaning towards
flash rom technology at the moment.
Anyone tips? Advice? Board layouts? Source code? ;-)

Christoph

1998\04\03@132448 by Michael Hagberg

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sounds like a fun little project to me.

i have a question about flash rom, when they are rated at 120ns is this for
the  read cycle time only? can you write data that fast or does it take
longer like eeprom data?

michael

-----Original Message-----
From: Christoph Klein <KILLspamhylaKILLspamspamMAYN.DE>
To: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Date: Friday, April 03, 1998 12:13 PM
Subject: Re: Looking for an easy ram buffer...


>Shawn,
>
>right now I am facing the same question. I am leaning towards
>flash rom technology at the moment.
>Anyone tips? Advice? Board layouts? Source code? ;-)
>
>Christoph
>

1998\04\04@064108 by wwl

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On Fri, 3 Apr 1998 12:20:31 EST5EDT, you wrote:

{Quote hidden}

Dallas do a chip, DS1280, which interfaces a 3-wire microwire bus to
up to 512K of SRAM - sounds just the job!
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1998\04\04@072224 by Don McKenzie

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Mike Harrison wrote:
{Quote hidden}

I just realized I also have a 256K DRAM to PIC16C74A Interface project
by Josef Hanzal in my dungeon as well, however I have designed with the
Dallas chip in the past and it does work great and really takes the hard
work out of hardware and software overhead.

Don McKenzie  RemoveMEdonspamTakeThisOuTdontronics.com   http://www.dontronics.com

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