You got lucky, as the 1225 chip behaves exactly like
the CMOS RAM chip that it contains... a 6116 type.. Your
EPROM programmer happened to do it accidentally right. It
wasn't on purpose as the FRAM didn't exist until a decade
later.
The FRAM is different, its CS is used to latch the address
lines... not to simply enable the bus drivers.
-Chuck Harris
Jan J wrote:
toggle quoted message
Show quoted text
I did encounter just that.... But I got around it by telling the Programmer it was a
1225 chip and all was fine
On 12/5/2017 9:29 AM, Chuck Harris wrote:
The Ramtron 16W08 family works very well in the 2465A and B
as both a replacement for the Dallas 1225, and as a replacement
for the battery and CMOS RAM in the "A" and early "B" scopes.
However...
Be warned that some EPROM programmers don't prime the pump
correctly with the FRAM chips. The CS is an address latch signal,
not a simple bus enable as it is with most RAM chips. This can mean
that your first, and last address will be in error, even though each
additional address will be fine.
In the 2465A or B scopes, the NVRAM is used as both an area to store
constants, and as system RAM. The system RAM controls the first
addresses as part of the interrupt vector array, and as such it is
restored every time the scope is powered up. Other instruments may
not do this.
To make the FRAM chips work happily in a scope with a separate battery
and CMOS RAM, you have to modify the battery test circuitry to fool
it into thinking the battery is always good.
( Short CR2371 and CR2370, replace CR2770 with 3.9K resistor, remove
battery, jumper + pad to - pad, install label over battery footprint
disclosing modification.)
-Chuck Harris
