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PICList Thread
'Static RAM'
1996\12\11@084625 by n Medical Technologies

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I'm a PIC newbie (but an EE oldie), and I am just starting to think
about a project based on a Microchip PIC.  I'll be needing to store up
to 10k or more of data, which will be accessed in a sequential fashion
(like a data logger)--take a reading, write to memory, take the next
reading, write to memory, and so forth.  When we're done taking data, it
will come out in the same way, that is, sequentially.

From what I've read, it seems that the traditional way to add memory to
a PIC is to use EEPROM, rather than SRAM or DRAM.  Now I know that DRAM
can be a pain, but is EEPROM preferable to SRAM for any particular
reason, beyond power considerations?

In my case, I'll be plugged into the wall, so I've got plenty of juice.
Has anyone had good or bad experiences with SRAM and PICs?  Any
particular models or interfacing methods?

Thanks in advance for your consideration.

Al Cohen
Boston Medical Technologies

1996\12\11@105914 by tjaart

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Boston Medical Technologies wrote:
{Quote hidden}

24C16 from Microchip. IIC interface and VERY cheap.

--
Friendly Regards

Tjaart van der Walt
______________________________________________________________
|  Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
|+27-(0)11-622-8686 |  http://wasp.co.za   | spam_OUTtjaartTakeThisOuTspamwasp.co.za |
|______________________________________________________________|

1996\12\11@113010 by Stephen H Alsop

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I use 8K serial eeproms type 24lc65 (8 can be used to give 64K)

Read them using the iic routines and only 2 i/o lines are used.

They can be read sequentially


----- Stephen H Alsop -----
email: .....s.ssystemsKILLspamspam@spam@easynet.co.uk
www  : http://easyweb.easynet.co.uk/~s.ssystems
S&S Systems Ltd, Bretton Court, Manor Road, Wales Village, Sheffield
S31 8PD, England.  Tel: 01909 773399  *  Fax: 01909 773645


----------
: From: Boston Medical Technologies <bosmedspamKILLspamUSER1.CHANNEL1.COM>
: To: Multiple recipients of list PICLIST <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
: Subject: Static RAM
: Date: 11 December 1996 13:47
:
: I'm a PIC newbie (but an EE oldie), and I am just starting to think
: about a project based on a Microchip PIC.  I'll be needing to store up
: to 10k or more of data, which will be accessed in a sequential fashion
: (like a data logger)--take a reading, write to memory, take the next
: reading, write to memory, and so forth.  When we're done taking data, it
: will come out in the same way, that is, sequentially.
:
: >From what I've read, it seems that the traditional way to add memory to
: a PIC is to use EEPROM, rather than SRAM or DRAM.  Now I know that DRAM
: can be a pain, but is EEPROM preferable to SRAM for any particular
: reason, beyond power considerations?
:
: In my case, I'll be plugged into the wall, so I've got plenty of juice.
: Has anyone had good or bad experiences with SRAM and PICs?  Any
: particular models or interfacing methods?
:
: Thanks in advance for your consideration.
:
: Al Cohen
: Boston Medical Technologies

1996\12\11@161029 by Robert Lunn

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>From what I've read, it seems that the traditional way to add memory to
>a PIC is to use EEPROM, rather than SRAM or DRAM.  Now I know that DRAM
>can be a pain, but is EEPROM preferable to SRAM for any particular
>reason, beyond power considerations?

       Serial E2 can be accessed with as few as two I/O lines without
       the need for external circuitry.

       E2 package dimensions are small.

       E2 will hold its contents during power-fail.

       E2 is cheap.

On the other hand...

       Reads from E2 are slow.

       Writes to E2 are v_e_r_y slow.

       Writes to E2 are limited to between 10^6 and 10^7 cycles.

For a data logging application, the write time and write endurance can be
the deciding factors.

___Bob

1996\12\11@174513 by TONY NIXON 54964

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My data logger uses CMOS 4040 ripple counters to generate the
addresses needed for 128K of external static RAM. This stores 64K of
12 bit data at a maximum rate of 10K samples per second. I used a
Dallas DS1245 RAM chip which has internal battery backup thus
eliminating the write delays with EEPROM.

I also needed to store configuration data into this RAM and the first
32 locations were used for this purpose. The hard part was to skip
these locations very quickly when the storage address wrapped around to
zero. I could not simply increment the counters 32 times as the 100uS
sampling rate would be compromised.

To overcome this I used a CMOS 4029 presettable counter. With this chip
I can set the outputs to any combination I like, with  a limit of 4
bits. Thus, when the data address wraps around I simply reset this chip and the
base address for the data becomes 20h instead of 0h.

Regards

Tony


Just when I thought I knew it all,
I learned that I didn't.

1996\12\12@022834 by Werner Terreblanche

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> From what I've read, it seems that the traditional way to add memory
> to a PIC is to use EEPROM, rather than SRAM or DRAM.  Now I know that
> DRAM can be a pain, but is EEPROM preferable to SRAM for any
> particular reason, beyond power considerations?

Al

 Usually the reason why people use EEPROM is because they want their
data to be non-volatile.  The drawback of normal EEPROMS are that
they require quite a long write cycle.

I would seriously consider looking at FRAM as well, if I were you.
It very reliable, software compatible with serial EEPROM but just
much much faster, because there is no writing cycle as in the case
with EEPROM.   This type of devices are the ideal replacement for normal DRAM
or SRAM, especially if you want it to be non-volatile.

Regards
Werner
--
Werner Terreblanche
EraseMEwterrebspam_OUTspamTakeThisOuTplessey.co.za (work)  OR  wernerspamspam_OUTaztec.co.za  (home)
Plessey SA, PO Box 30451, Tokai 7966, Cape Town, South Africa

Check out my Variometer Kit on:
 www.aztec.co.za/users/werner/variokit.htm
-------------------------------------------------------------

1996\12\12@173711 by Dave Mullenix

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Werner Terreblanche wrote:

>I would seriously consider looking at FRAM as well, if I were you.
>It very reliable, software compatible with serial EEPROM but just
>much much faster, because there is no writing cycle as in the case
>with EEPROM.   This type of devices are the ideal replacement for normal DRAM
>or SRAM, especially if you want it to be non-volatile.

What is FRAM?

Thanks, Dave

1996\12\17@140911 by Dorin Dogaroiu

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Draga taticule,
N-am de fapt nimic de zis, decat ca probabil si cu ajutorul lui
Dumnezeu, ii va iesi tot media 5 si la Romana lui Petru. Horea a
fsacut asa-si-asa la fizica la teza. M-am luptat toata saptamana
cu Vali, sa dea niste bani pe care ii datora Mariei Titeica pentru
o traducere. E intr-adevar zgarcitulet bine de tot; multa lume
zice ca asta e secretul pentru care are bani si sittuatie. Se
poate. Nu-l condamn, mai ales eu care nu sunt in stare sa tin banii
de loc. Cat despre Maria Titeica, nu stiu daca ti-am povestit mare
lucru. E oricum, un fel de d-na Sasu de nivel cu mult mai ridicat.
Adica are probleme psihice mari, dar are un cap extraordinar si
evident ca asta o ajuta. Munca mea de sora de caritate e cu mult
mai usoara in cazul asta. Iti dai seama, ca dde cand s-a facut bine
d-na Sasu (i-am facut rost si de loc de munca, lucreaza la Oncologie
la farmacie) eu sunt intr-un somaj tehnic de nedescris. Noroc ca
azi mi-a venit o idee de milioane. Am insa mila fata de tine si nu
ti-o comunic si mai ales n-o pun in aplicare pana nu vii si tu
aici, sa discutam inainte. Sper sa nu lesini chiar de tot cand ai
sa auzi ce vreau sa fac.Altceva nu mai stiu ce as putea sa spun.
YToate sunt destul de bune si frumoase, slava Domnului. Incep sa
am atat timp liber, ca nu mai stiu ce sa fac cu el. Pana una alta,
sa-l tina Dumnezeu pe Vali cu toata zgarcenia lui cu tot, ca m-a
ajutat inclusiv sa-mi optimizez munca asa fel incat sa fiu
groaznic de eficienta. Te cam pupam,
diana & copiii.

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