Very possible that I damaged the tuning forks, as I wasn't aware how fragile they are.
As a follow up to my experiences, I purchased a DS12887+ from seller ergah
on Ebay for $4.25 + $1.93 shipping. It arrived after I had the problem corrected, but I thought I'd try it anyway.
The date code was 1419F (?19 week of 2014). It plugs in directly to the DS12285 socket with no changes (the xtal and battery pins are N/C on the DS12887+).
It arrives with 00H programmed into register "A" , but writing an AAH to register 0AH using Z-RTC.COM (thanks Frank for pointing this out earlier!) started it up.
With the DS12885+ selling for $7.31 (Mouser), this is actually a bit less expensive, and the battery should be good for 10 years.
Just another solution if anyone else encounters the same problems I did.
On Wednesday, July 16, 2014 2:37:14 PM UTC-4, gek...@gmail.com wrote:
I'm pulling out my hair trying to access the DS12885 RTC on the MSDOS Support PCB.
The rest of the board (timer, interrupt and EPROM) appears to be functioning properly. I have not tried the mouse/keyboard section yet.
I can see low pulses on Pins 14/17 as expected. I'm using the "E" command from the 8088 board for testing time/date in V10.3 of John's monitor software.
When I set the time the seconds and day will program, but the hours/minutes/year/month remain gibberish. I also get errors when entering the "X" MSDOS menu - either that the RTC is stuck or that invalid BCD data exists.
I've swapped TTL and DS12885. I've also changed the 32.768khz xtal. When I scope pins 2/3 on the DS12885 (XTAL) I can see somewhat noisy pulses.
Would the DS12885 at least store the date if the xtal isn't oscillating properly? It looks like the RTC shares most of the same address/data circuitry with the other sections. The 8088 has a 8 mhz clock, could speed be an issue?
Any thoughts or hints appreciated!