CMOS system options don't persist on cold boot after DS12887 replacement

[matt.c]

Thanks T-R-A and Ruud, I appreciate you taking the time to help a lurker who hasn't posted much! It seems I inadvertently left some information out due to sheer ignorance.

Thanks for your response, glitch! It seems you are correct, pin 21 is missing on my original Dallas module. I also have some pictures of the board I took while it was out of the case and I can see there is a connection to pin 21 to a trace that goes through a via, so I bet you're correct that it's being held by whatever it eventually connects to.

I don't have the stamina or inclination to take out the board and snip the pin tonight, but I will give this a shot Saturday morning and update this thread accordingly. I don't want to celebrate prematurely, but I'm feeling soo much better about all this now. At least I have a thread to pull on.

[glitch]

Yeah, I've personally had this happen to me, that's how I know about it

[matt.c]

I had some time tonight and I was able to get in there and safely snip pin 21. Everything saves now!!!

I really wish I had taken a closer look at the data sheet, this was staring right at me.

datasheet.jpg

Thanks all!

[JimWest]

I replied via PM, but I'll post here as well: a likely cause is that the original chip was one of the Dallas modules that didn't have the "clear CMOS" pin. Some motherboards will tie this position to ground or use it to route another signal if they used a full 24-pin DIP footprint. The solution is to cut off the pins that are not required for your situation: easiest thing to do is match the missing pins on the original module. Just snip them off the GW-12887-1 or bend them up if you don't want to cut.

I just stumbled across this forum and this post. Thank you for the information! I had exactly the same problem. Removing the unnecessary pins solved it.