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

Jean-Pierre Desrochers jpdesroc at oricom.ca
Sun Apr 25 16:56:59 CEST 2021


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.



 

The specs say it is full Dallas DS1225 compatible.

There are many sites who show how to hack a DS1225 package
to disconnect the inner battery tabs and connect small leads
to an external battery keeping the still working SRAM.

This for example:

https://www.google.com/url?sa=t
<https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwi
Dl_DKzZnwAhVdElkFHZaBCTsQFjABegQIAhAD&url=http%3A%2F%2Fworldphaco.com%2Fuplo
ads%2FTEKTRONIX_2465b_OSCILLOSCOPE_CALIBRATION___REPOWERING_THE_DS1225.pdf&u
sg=AOvVaw1WP8nMcsFuEALX2uMw2rP1>
&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiDl_DKzZnwAhVdElkFHZaBCTsQFjABegQ
IAhAD&url=http%3A%2F%2Fworldphaco.com%2Fuploads%2FTEKTRONIX_2465b_OSCILLOSCO
PE_CALIBRATION___REPOWERING_THE_DS1225.pdf&usg=AOvVaw1WP8nMcsFuEALX2uMw2rP1


Since my chip is a M48Z18-100PCI it does not have the same 
potted packing of a genuine DS1225 (should it ??) so dremeling it
to reach the battery tabs would be quite hazardous..

 

So here is my question:

I'd like to build a small 28 pins 600mils DIP pcb
who would contain a 8Kx8 SRAM with battery controller IC
the same way the inside DS1225 does it:



DS1218 and DS2064 are now obsolete ICs so this would not be a good choice..

 

A company called Glitch Works has this type of new substitute IC available:

 
<https://www.tindie.com/products/glitchwrks/glitch-works-gw-1225-1-dallas-ds
1225-replacement/>
https://www.tindie.com/products/glitchwrks/glitch-works-gw-1225-1-dallas-ds1
225-replacement/

But for me $51.00US including shipping to Canada is too expensive..

But the idea of a small 28 pins DIP pcb module is a good one..
Building it would be fun too !

I'm not an engineer and cannot figure out the DS1225 read/write needs to be
taken care of
choosing the right components. Any 8Kx8 SRAM with a 100ns acquisition should
do
but the choice of a good battery controller IC and the adequate connections
between both IC's
and the 28 DIP pins to behave exactly like a M48Z18 or DS1225 exceeds my
knowledge..

Can you help with some possible IC's and some easy wirings linking them ?

Many thanks !

 

 

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