gnupic: Q - serial RAM chips?
Subject:
Re: Q - serial RAM chips?
From:
####@####.####
Date:
30 Dec 2004 11:13:29 +0000
Message-Id: <5059.1104405180@www36.gmx.net>
Use the ramtron fram devices , you can order free samples on there website.
The newer A types support up to 1 Mhz i2c speeds, the old types are rated
for
400 Khz. As i remember, up to 256 Kb is available for i2c, on spi, up to 1
Mb
with greater speed. The chips comes in a 8 pin, but there has discontinued
the
dil product line and so you must use the 8 pin soic smd ic.
This type of ram retain the information without power similar to eeprom and
are
rated to 10 Years of data retention.
The chips are pin compatible with EEproms of the same types, so it's
advisable to
design the pbc in order to have the possibility to place a 8 pin dil eeprom,
or a
smd 8 pin soic inside the dil area. This gives the possibility to use other
suppliers.
If you use different hardwired addresses for the dil/soic pbc, then its
possible
to expand the eeprom/fram using a dil on top of the soic part, socket or
directly soldered.
The eeprom is cheaper then fram. It depends on the application,
normally especially larger eeproms have paging ram in order to speed up the
writing.
The biggest parts have 256 bytes of paging ram , other parts have 64/16/0
paging ram.
This signifies, that the eeprom needs 5 ms to write 1/16/64/256 bytes of
data.
With 256 bytes of paging ram is possible to stream data without waitstates
at 400 kb/s. Some care must be made for the paging mode on the firmware.
It's clear, that the 1 Million write/erase cycles takes a limit to the usage
of eeproms.
I know some applications, that uses 256 Kb eeprom and logical paging in
order to archive the required erase/write cycles for a 16/32 Kb logical
eeprom, because it's cheaper then using frams. For hobbistic applications,
the difference of 3$ don't
really matter. On the other side, for micro power application, frams are
ideal.
> Hi,
>
> Can anyone please recommend a serial RAM chip, preferably 16k-64k+, in a
> low (preferably 8) pin count? Preferably I2C compatible?
>
> All I've found so far that's I2C compatible is the Philips PCF8570, but
> it's only 256 bytes - barely worth the trouble.
>
> All recommendations gratefully appreciated
>
> --
> Cheers
> David
>
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