MSDOS Support V2 PCB RTC problem.

[geka...@gmail.com]

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!

- Gary