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'Such a thing as serial SRAM?'
1998\05\06@230505 by Bob Newhart

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Does anyone know of a serial static RAM I could use for additional PIC
data memory?  I am attempting to alter a pre-existing design that uses
93C66 EEPROMs, so something with the same pinout and bit-banging scheme
would be nice, although not absolutely necessary.  I don't care whether
the SRAM is volatile or not.

The only firm requirements are three pin interface, minimum 64 bytes RAM
per chip (bigger is better), and no write cycle limitations like those
associated with EEPROM and FLASH.

Bonuses would be:
    256 bytes per chip
    nonvolatile
    8 pin package with pinout similar to 93C66 EEPROM

I have searched extensively already, and all that I've found are some
XICOR non-volatile SRAMs that aren't large enough, and a variety of
parallel parts (including the Dallas RAMPort).  It seems like something
like this should exist.  Am I missing something obvious?

Oh, I also spoke with a Microchip tech support guy who told me he's had
the same problem and was also unable to find a solution.

Any help would be greatly appreciated!

Jason Harris

1998\05\06@235230 by robert bowman

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From: Bob Newhart <spam_OUTsmegtraTakeThisOuTspamGOODNET.COM>


>Does anyone know of a serial static RAM I could use for additional PIC
>data memory

probably not what you want to hear, but I have been able to glue together
74LS164s and 74LS165 to emulate serial devices of whatever size you want.
not at all pretty, and there must be a better solution.

1998\05\07@002537 by Dennis Plunkett

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At 09:35 PM 6/05/98 -0600, you wrote:
>From: Bob Newhart <.....smegtraKILLspamspam@spam@GOODNET.COM>
>
>
>>Does anyone know of a serial static RAM I could use for additional PIC
>>data memory
>
>probably not what you want to hear, but I have been able to glue together
>74LS164s and 74LS165 to emulate serial devices of whatever size you want.
>not at all pretty, and there must be a better solution.
>
>

Yes there is Xicor may have an SPI type part, but some years ago Phillps had
an I2C static ram with 256 bytes if I remember correctly



Dennis

1998\05\07@002548 by Dennis Plunkett

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At 08:02 PM 6/05/98 -0700, you wrote:
{Quote hidden}

If I remember correctly, Philips had an I2C SRAM or around 256 bytes. Your
other option is shift registers, or perhaps another PIC

Dennis

1998\05\07@010158 by tjaart

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Dennis Plunkett wrote:

> At 08:02 PM 6/05/98 -0700, you wrote:
> >Does anyone know of a serial static RAM I could use for additional PIC
> >data memory?  I am attempting to alter a pre-existing design that uses
> >93C66 EEPROMs, so something with the same pinout and bit-banging scheme
> >would be nice, although not absolutely necessary.  I don't care whether
> >the SRAM is volatile or not.
> >
> >The only firm requirements are three pin interface, minimum 64 bytes RAM
> >per chip (bigger is better), and no write cycle limitations like those
> >associated with EEPROM and FLASH.
> >
> >Bonuses would be:
> >     256 bytes per chip
> >     nonvolatile
> >     8 pin package with pinout similar to 93C66 EEPROM

PCF8583 buys you 240 bytes of SRAM as well as a clock/calendar.

--
Friendly Regards

Tjaart van der Walt
tjaartspamKILLspamwasp.co.za

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1998\05\07@014735 by Mike Keitz

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On Wed, 6 May 1998 20:02:01 -0700 Bob Newhart <EraseMEsmegtraspam_OUTspamTakeThisOuTGOODNET.COM>
writes:
>Does anyone know of a serial static RAM I could use for additional PIC
>data memory?  I am attempting to alter a pre-existing design that uses
>93C66 EEPROMs, so something with the same pinout and bit-banging
>scheme
>would be nice, although not absolutely necessary.  I don't care
>whether
>the SRAM is volatile or not.

Look at the Ramtron FRAM's.  These are intended to drop in in place of
EEPROM (both Microwire and IIC models available), but write "instantly"
like RAM and withstand more cycles (10^12 cycles IIRC).  However, unlike
EEPROM, read cycles will wear the device out just like write cycles do.
Unless you're reading constantly, they should last long enough.  The
stored data is easier to glitch than EEPROM, but you don't care about
that.  Also they only work up to temperatures of 85C, period.

>
>The only firm requirements are three pin interface, minimum 64 bytes
>RAM
>per chip (bigger is better), and no write cycle limitations like those
>associated with EEPROM and FLASH.
> It seems like
>something
>like this should exist.  Am I missing something obvious?

Yes it really should.  It's apparently not a very marketable idea for
whatever reason.

I think Dallas makes a converter chip to interface to a "commodity" SRAM
chip, but that's only practical for many Kb of storage.  National used to
have some small serial RAMs in its COP4 series.  Digikey lists the COP498
"RAM and Timer" but I forget how much RAM it has.  I think it is serial.

>
>Oh, I also spoke with a Microchip tech support guy who told me he's
>had
>the same problem and was also unable to find a solution.

Why not replace the PIC with one having more RAM, especially if you only
need 64 bytes there are several possibilites.  The PIC 16C622 or
PIC16C558 offer 128 bytes RAM in an 18-pin size.

Since Microchip may be listening, I'm still lobbying for a PIC with about
2K of SRAM built in.  The SRAM can be a peripheral module, accessed via
SFR's for address and data.  There should be two sets of address and data
SFRs to allow working in two places in the RAM at once.  It would be nice
if the address SFR had auto-increment and/or decrement capability.


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1998\05\07@152316 by Dwayne Reid

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>Does anyone know of a serial static RAM I could use for additional PIC
>data memory?  I am attempting to alter a pre-existing design that uses
>93C66 EEPROMs, so something with the same pinout and bit-banging scheme
>would be nice, although not absolutely necessary.  I don't care whether
>the SRAM is volatile or not.
>
>The only firm requirements are three pin interface, minimum 64 bytes RAM
>per chip (bigger is better), and no write cycle limitations like those
>associated with EEPROM and FLASH.

Silly thought, I know, but how about a 12c671?  128 bytes of RAM - you may
be able to use all of that if you can get your bit banging i/o to run using
ADRES, FSR, and whatever other registers that might be available.  Only
question is cost and availability.



Dwayne Reid   <dwaynerspamspam_OUTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, Alberta, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1998\05\09@032157 by g.daniel.invent.design

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Jason, others,
Dallas make an iButton part with 64k bits N.V. ram,
horrendously expensive, 1 signal wire. parts also have a "turbo mode"
but this still has some limitatations.

code is DS1996

regards Graham Daniel

Dennis Plunkett wrote:
{Quote hidden}

1998\05\09@113639 by Geoff Smith

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I found serial rams from Ramtron, http://www.ramtron.com. They go upto 16kbit are
nonvolatile, but have no write cycle delay and are good for 10 million
writes. I have not used them other than tests.  Has anyone comments? I
think the part cost on 1-off is around $3-5

Geoff.

{Quote hidden}

1998\05\11@081905 by Pavel Korensky

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At 21:35 6.5.1998 -0600, you wrote:
>From: Bob Newhart <@spam@smegtraKILLspamspamGOODNET.COM>
>
>
>>Does anyone know of a serial static RAM I could use for additional PIC
>>data memory
>
>probably not what you want to hear, but I have been able to glue together
>74LS164s and 74LS165 to emulate serial devices of whatever size you want.
>not at all pretty, and there must be a better solution.
>

I used PCF8583 (Philips) in one of my projects. This is the inexpensive
circuit with date, clock, alarm and 240 bytes of RAM. Chip use I2C bus, so
you will need couple of free bytes in PIC for I2C implementation. You can
use up to 2 chips on one bus, so you can have up to 480 bytes of RAM. Clock
and/or event counter is a free bonus. Price of the chip should be somewhere
around 3 - 4 dollars.
I used these chips with MAX690 watchdog, so you can have battery backup
SRAM with this chip and one lithium button.

Best regards

PavelK

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1998\05\11@083147 by Pavel Korensky

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At 20:02 6.5.1998 -0700, Bob Newhart wrote:
>Does anyone know of a serial static RAM I could use for additional PIC
>data memory?  I am attempting to alter a pre-existing design that uses
>93C66 EEPROMs, so something with the same pinout and bit-banging scheme
>would be nice, although not absolutely necessary.  I don't care whether
>the SRAM is volatile or not.
>
>The only firm requirements are three pin interface, minimum 64 bytes RAM
>per chip (bigger is better), and no write cycle limitations like those
>associated with EEPROM and FLASH.
>
>Bonuses would be:
>     256 bytes per chip
>     nonvolatile
>     8 pin package with pinout similar to 93C66 EEPROM
>

As I already wrote. I used PCF8583 in one of my projects. These chips are
date/clock/alarm chips with 240 bytes of RAM and I2C interface. You can use
up to 2 chips on one I2C bus, so you can get 480 bytes of RAM. Clock and/or
event counter is a free bonus. I also used MAX690 as a watchdog chip, with
one small lithium battery as a backup for RAM content. Works without any
problem. Only sad think is that you need place for I2C routines.

Best regards

PavelK

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* Pavel Korensky                                                         *
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* Modranska 1895/17, 143 00, Prague 4, Czech Republic                    *
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* PGP Key fingerprint:  F3 E1 AE BC 34 18 CB A6  CC D0 DA 9E 79 03 41 D4 *
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