[sdiy] Substituing M48Z18-100 (equ of DS1225AB-100) with 28 pins DIP small pcb

Steve Lenham steve at bendentech.co.uk
Mon Apr 26 13:02:03 CEST 2021

On 25/04/2021 15:56, Jean-Pierre Desrochers wrote:
> Hi list,
> I need to replace a M48Z18-100PCI (8K x 8 battery backed SRAM) in one of 
> my old
> test equipment. It's dated 1996 so It's inner battery life is ending.
> Yeah even after 25 years it still keeps its data.. (!!!)
> It's a 28 pins 600mil DIP package.

Bearing in mind that we are all on this Earth for but a short time, it 
seems to me that the best replacement for the M48Z18-100PCI would be a 
brand new M48Z18-100PCI, since they are still in production and 
available from mainstream distributors e.g. Farnell.

Save your precious time for something more important!

If you actively WANT to experiment with FRAMs then that is a different 
matter. I did something similar recently and there was a thread about it 
not so long ago. In a nutshell, the 5V parallel FRAMs are ALMOST a 
drop-in replacement for SRAMs, but they have particular requirements for 
/CE timing. The vital thing to know is that the FRAMs latch their 
address on the falling edge of /CE, which means:

a) you must have one /CE pulse for every FRAM access, since address 
changes while /CE is held low will not be registered.

b) the address needs to be valid before /CE is asserted.

These conditions are often met, but not always, which means you need to 
know at least a little about the circuitry and timing of the equipment 
in which you want to retrofit the FRAM.

Hope this helps,

Steve L
Benden Sound Technology

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