Gary, just rechecked mine (been a long time since I was there!). The clock seems fine for time and date. Was many months ago since I set it. The only thing I see an error with is the century (“20”) came up as ?? so it read as ??14/07/16
When I reset the date it appears OK i.e. as 2014/07/16. On reset and power down it comes back correctly as 2014. Not sure what the problem is/was.
Sorry don’t have a suggestion for you. Hope it is the crystal.
John
From: n8ve...@googlegroups.com [mailto:n8vem...@
googlegroups.com ] On Behalf Of gek...@gmail.com
Sent: Wednesday, July 16, 2014 11:37 AM
To: n8ve...@googlegroups.com
Subject: [N8VEM-S100:4612] MSDOS Support V2 PCB RTC problem.
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--
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