Hi all,
Gabriel D. <[EMAIL PROTECTED]> wrote:
> SRAM = Static-RAM , doesn't need any power to keep data, but only to change
> the stored bit value. I'm sure you can find lot of information about SRAM
> (AFAIK called FLASH in some commercial products) functionning.
You got some things confused here: SRAM only needs 'ordinary' power
when used (reading/writing), and because it's static, 'none' when not
used. That 'none' power is only in principle. It does need to keep
its supply voltage, and in practice does use SOME current, to keep
its contents.
Modern SRAM's work near-perfect in this respect, and there are
sometimes specially selected/produced low power types. For such a
SRAM, a simple battery can maintain a supply voltage for years (like
a CR2032 3 Volt Lithium battery), where an important factor becomes
the discharging of the battery itself. These days, for some purposes
there are even some type of 'super-capacitors' (GoldCaps is a common
name) that can do this. When the SRAM is used, ofcourse it will need
an ordinary power supply, instead of the backup.
Memory IC's that really don't need ANY power supply to keep their
contents, are ROM (contents put in there when manufactured), and
EPROM. The main disadvantage an EPROM has when compared with
battery-backupped SRAM, is that it can only be re-written a limited
number of times, usually in the order of a couple of thousand times.
This also mostly needs to happen outside the system it's used in.
For SRAM, such a limit doesn't exist (well, until it goes broke). Big
advantage for EPROM's on the other hand, is that they don't
need such a power supply backup.
For 'normal' EPROMs erasing is done by ultra-violet light, and the
glass window in the EPROM shows it to be such a type.
Flash memory is in essence similar to EPROM, but can be erased
electrically, so these don't need, and thus don't have such a glass
window.
FInally, there's even PROM, this is essentially EPROM as well, but to
keep it cheap, this is put into ordinary glass-less IC packages. That
makes them cheaper to produce, but because they miss that glass
window, they can't be erased with ultra-violet light, and so they can
only be programmed once.
If you want to know more about these, there's plenty of reading
material on this available from the manufacturers of such IC's, like
Intel, AMD, Texas Instruments, .....(some 50 or 100 more to choose
from)
Greetings,
Alwin Henseler ([EMAIL PROTECTED])
http://huizen.dds.nl/~alwinh/msx (MSX Tech Doc page)
http://www.twente.nl/~cce/index.htm (computerclub Enschede)
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