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'[PIC]: Serial RAM for 16F84?'
2000\12\03@124916 by Wojtek Zabolotny

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Hi All,

Could someone please suggest me a cheap RAM (at least 4kB) with serial
interface (SPI or I2C) which could be connected to the 16F84?
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                       Wojciech Zabolotny
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2000\12\03@135215 by Andy N1YEW

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24C64

Andy N1YEW
----- Original Message -----
From: "Wojtek Zabolotny" <spam_OUTwzabTakeThisOuTspamISE.PW.EDU.PL>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Sunday, December 03, 2000 5:50 AM
Subject: [PIC]: Serial RAM for 16F84?


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2000\12\04@050437 by dr. Imre Bartfai

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Hi,
AFAIK 24C64 is an EEPROM not a RAM, it means one should waits approx. 5
msec until write is completed (or ACK polling is o.k. too). I know only
one true RAM: PCF8570 if I recall, but it is only 256 byte. I desperately
seek also a solution.

Theoretically, there is a possible workaround:
take a SRAM (e. g. 6264) and fit to a PIC, which has an I2C connection to
the world. It is surely doable (I did it), but needs a lot of area on PCB
and some additional components.

Any further ideas?

Regards,
Imre


On Sun, 3 Dec 2000, Andy N1YEW wrote:

> 24C64
>
> Andy N1YEW
> {Original Message removed}

2000\12\04@082858 by Andy N1YEW

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a 6255? it is a FMAG RAM.

Andy N1YEW
----- Original Message -----
From: "dr. Imre Bartfai" <rootspamKILLspamPROF.PMMF.HU>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Monday, December 04, 2000 5:03 AM
Subject: Re: [PIC]: Serial RAM for 16F84?


{Quote hidden}

inside
{Quote hidden}

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2000\12\04@090307 by mike

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On Mon, 4 Dec 2000 11:03:04 +0100, you wrote:

>Hi,
>AFAIK 24C64 is an EEPROM not a RAM, it means one should waits approx. 5
>msec until write is completed (or ACK polling is o.k. too). I know only
>one true RAM: PCF8570 if I recall, but it is only 256 byte. I desperately
>seek also a solution.
>
>Theoretically, there is a possible workaround:
>take a SRAM (e. g. 6264) and fit to a PIC, which has an I2C connection to
>the world. It is surely doable (I did it), but needs a lot of area on PCB
>and some additional components.
>
>Any further ideas?
This has come up a number of times, and the answer has always been
that there isn't one. There just isn't a market for such a device, once you discount all the
applications that could use an eeprom, parallel SRAM or DRAM.
The easiest and cheapest way would be to use a conventional SRAM or
DRAM, possibly with external latches and/or address counters. If
you're short on pins or space, remember that quite big SRAMS are
pretty cheap, in fact I don't think you can readily buy anything
smaller than 32Kbytes any more, so you may be able to save pins by
using a larger SRAM and not using all the data pins - address pins are
more 'productive' in that each extra one doubles the addressable
range.
If space is an issue, I think several makers do SRAM in uBGA type
packages.

I think Dallas make a device to serialise and nonvolatalise a parallel
SRAM to work on a SPI bus, but a descrete or second-PIC solution will
usually be much cheaper.
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2000\12\04@094958 by Michael Rigby-Jones

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{Quote hidden}

OTOH for each data pin you lose, you halve the amount addressable data, so I
don't think either is more productive really!

Mike

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2000\12\04@101618 by jamesnewton

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I have some SPI serial memory listed at
http://www.piclist.com/techref/mem/spi.htm
I think your best bet out of those is FRAM
http://www.ramtron.com/products/brochure/brochure.htm

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{Original Message removed}

2000\12\04@123754 by Dan Michaels

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Imre wrote:
........
>Theoretically, there is a possible workaround:
>take a SRAM (e. g. 6264) and fit to a PIC, which has an I2C connection to
>the world. It is surely doable (I did it), but needs a lot of area on PCB
>and some additional components.
>
>Any further ideas?
>

parallaxinc.com has a small SRAM board with RS232 I/F and 8KB
SRAM standard. Expensive at $30+ [but Stamp users would appear to
have loads and loads of $$$].

Also, I produced a couple of PIC<->SRAM boards last summer. One
I have for sale as a complete PIC40 SBC.

The other project I never finished the firmware for --> pcb is
1.75"x2.5" [44x64mm], has layout for two 32KByte PDIP SRAMs,
16C64/74, and 15-pin header so the RAM is accessible by
RS-232/I2C/SPI comm, or directly on 8 parallel datalines + control
signals. Basically an extension of the parallax concept. If anyone
wants to roll their own PIC40 firmware, I have 10 of these pcbs
available - cost me $8/each from APCircuits  - add a little markup.

best regards,
- Dan Michaels
Oricom Technologies
http://www.oricomtech.com
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2000\12\04@135215 by mike

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On Mon, 4 Dec 2000 14:46:40 -0000, you wrote:

{Quote hidden}

Not true - to double the capacity you have to either double the number
of data pins, or add one address pin - going from one data line to two
is the only case where it makes no difference -  it's diminishing
returns from then on. e.g. adding 2 pins to the data bus doubles the
capacity but adding 2 address pins quadruples it.

An extreme example - for 16 pins, you can do 32K x 1 bit = 4kbytes, or
256 x 8 bits = 256 bytes.
Obviously there is an access time penalty, but big and narrow easily
wins over short and wide for capacity.

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2000\12\04@141714 by Byron A Jeff

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>
> a 6255? it is a FMAG RAM.

Just be aware that Ferro-Magnetic memories are worn down on reads too and
not only writes. So you read it too many times and it wears out.

Somthing like 10 million read/writes IIRC.

BAJ

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2000\12\04@144142 by Alexey Vladimirov

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04 Dec 00, Byron A Jeff writes to All:

P> Just be aware that Ferro-Magnetic memories are worn down on reads too and
P> not only writes. So you read it too many times and it wears out.

Correct.

P> Somthing like 10 million read/writes IIRC.

Wrong. Ramtron quote 10 billion read/writes. 1000 times more, than
10 million... Check

http://www.ramtron.com/products/appnotes/RAMexpansion.pdf

for endurance considerations. Data retention for FRAM also depends from the
external temperature, check
http://www.ramtron.com/products/appnotes/data%20retention%205-00.pdf

for more details.

You can also buy FRAM memory on-line, for example at http://www.svtehs.com

Alexey
RemoveMEavladspamTakeThisOuTsvtehs.com

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2000\12\07@012342 by Harold Hallikainen

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       This has been a frequent topic of discussion.  You may want to check the
archives. As far as I know no serial RAM over a few hundred bytes exists.
There are other serial memory architectures available, but they generally
suffer from lack of speed or limited number of writes. I finally just
went to parallel static RAM and latches to latch out the addresses.

Harold


On Sun, 3 Dec 2000 11:50:21 +0100 Wojtek Zabolotny <wzabEraseMEspam.....ISE.PW.EDU.PL>
writes:
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FCC Rules Online at http://www.hallikainen.com/FccRules/

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