Thanks for the response. If endeavoring to do this (rtc + ram), there are already a number of folks that claim to have working solutions, so I would search out their progress and find the flaws and try to find elegant workarounds. The easiest way is to find compatible no-batt rtc, and add logic around that to extend the ram. Maybe easiest is to used the latest version of the original MC148616 and i/f logic and add an fram if the are any parallel i/f available - the original has muxed a/d so that would have to be demuxed. Goal would be to try to get away with a bunch of glue logic in an XC9536 or 72. To try to recreate the ds1486 from scratch would take a tremendous verification/validation effort with no payback. Seems like a lot of nuances present. Mot's original MC14xx had battery discharge bugs which was one of the Dallas popularities. Mot fixed it in the b version.
Most modern designs use an i2c rtc and an fram. So, other than legacy sockets, not much market.
pmoyle
