[sdiy] SRAM question

[Tom Wiltshire]

I second what Dave says below. This is a good summary. My own  
experience of this comes from changing backup batteries in my Korg  
Polysix. The schematics of the Polysix would give you a practical  
example.

T.

On 19 Feb 2010, at 17:57, David Brown wrote:

> The S in SRAM stands for static.  It does not need to be  
> refreshed.  A battery will keep the ram powered on.  Some type of  
> circuit is typically needed to power the ram from the logic supply  
> when on.  On older 5 volt systems, often times the battery would be  
> at a lower voltage, say 3.75 volts.  A couple of diodes would be  
> used to form an "or" between the battery and logic voltage.  This  
> makes sure that none of the input signals are ever at a higher  
> voltage than the ram.  If the battery was rechargable, then the  
> charging circuit could provide this function.
>
> Since the ram is kept alive, special attention is needed on the  
> inputs so a random write does not occur on power down or power up.   
> Sometimes pullup resistors are added to the inputs to make sure  
> they are pulled "down" on power down to reduce power consumption.   
> Very special attention is given to the write signal to make sure it  
> doesn't glitch.  Sometimes this can be a specific driver that  
> behaves well, or in some cases, a signal is provided from the power  
> supply that indicates mains voltage has been lost.  This signal can  
> be used to qualify the write signal.
>
> Dave
>
> At 09:36 AM 2/19/2010, cheater cheater wrote:
>> I think the SRAM doesn't need to be refreshed? So basically you just
>> keep voltage to the chip and that's it.
>>
>> But, bear in mind I know nothing of electronics. =)
>>
>> D.
>>
>> On Fri, Feb 19, 2010 at 18:25, Ian Smith  
>> <taciturn_unquiet at hotmail.com> wrote:
>> >
>> > Hey all,
>> >
>> > For those of you that are still here and haven't unsubed and  
>> gone over to the yahoo list, I have a question about SRAM chips  
>> and batteries for memory.
>> >
>> > How exactly does this work? using a battery to retain the data  
>> saved in the chip?
>> >
>> > Thanks,
>> >
>> > Ian (still here) Smith
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