SRAM chips

[Jeroen Proveniers]

> -----Original Message-----
> From: Fraser, Colin J [mailto:colin.fraser at calanais.com]
> Sent: Saturday, August 19, 2000 6:29 PM
> To: 'Jeroen Proveniers'; 'Synth DIY'
> Subject: RE: SRAM chips
> 
> 
> > -----Original Message-----
> > From: Jeroen Proveniers [mailto:J.Proveniers at orga.nl]
> > Sent: Friday, August 18, 2000 2:08 PM
> > To: 'Synth DIY'
> > Subject: RE: SRAM chips
> > 
> > 
> > An DALLAS DS1244 32K SRAM with backupbattery could also be 
> > considered. This
> > is a module slighty bigger dan DIP-28 and has an onboard 
> > lithium battery
> > that should last 10 years. Advantage of such module is that 
> > it contains
> > protection circuits to prevent inadvert writes at power 
> > up/down. These units
> > are reliable, but rather expensive. One thing, you know it's 
> > guaranteed to
> > work.
> 
> I find the intergrated battery backed RAM chips to be very expensive.
> I prefer to use the Dallas DS1210 battery backed RAM controller.
> This is an 8 pin device that provides automatic switching of 
> the RAM Vcc on
> power down.
> It also buffers the CE pin for the RAM access, and write 
> protects the RAM as
> soon as the main power supply drops below 4.75v
> Further, it has inputs for 2 batteries to provides resilient 
> backup in the
> event of a battery failure.
> It also has another neat trick - if the battery voltage is 
> below a nominal
> level, after power-up, the second access to the protected RAM 
> device will be
> blocked.
> This allows you to implement code that writes a byte in memory after
> start-up, then writes a different value to the same location.
> If the battery is low, the second write will fail, so your 
> can detect in
> software that the battery needs replacing and warn the user.
> These chips cost about 3ukp, add another typical 3ukp for a 
> 62256 and you're
> still a lot cheaper than the equivalent integrated BBSRAM.

There's also a DS1216 or so, which is just a socket which the chip you
describe and a battery (SmartSocket). But they're indeed very expensive.
Another option which involves no batteries at all would be to NOVRAM, I'm
sure if I'm right on the name, but that RAM which built in E2PROM cells next
to each SRAM cell. At poweroff the copy the contents of RAM to E2PROM. Only
needed extra is a big capacitor.

JJ