Hi Gary, Good to hear that you got the RTC working, I've been watching this thread with interest, my board will be completed sometime next month. It seems odd that more than one person is having issues with the RTC chip and it got me thinking. According to the datasheet the RTC clock circuitry has been designed for a 6pf load capacitance 32.768khz crystal, the Abracom AB38T-32.768KHZ is specified on the Mouser site as 12.5pf, in fact 32.768khz crystals seem to be available in load values from 6pf all the way upto 18pf. I'm not sure how touchy the RTC is but it may be worth bearing this in mind and searching out a 6pf load capacitance crystal. regards David Fry
On Friday, July 25, 2014 12:47:05 PM UTC+1, [email protected] wrote: > Success!!! > > Removed the keyboard/Timer/Interrupt sections, no change. > Looking at the "A" register, and programmed with with 0AAH, it reads back > as 2AH. I then noticed that the clock was advancing erratically, eg 1 > second forward every 20-30 seconds. > Swapped the xtal for the 4rd time, and all started working! > > My first two xtal's were Abracom AB38T-32.768KHZ from Mouser, the third > was a LP49 type from Ebay (Pletronics LP490071-32.768M. The last xtal was > pulled from a kitchen timer. > > I don't want to jinx myself and substitute back one of the Abracom xtals > to see if they were really defective - or if Frank's programming hint fixed > the problem. It's sure nice to see it working. > > Thanks to all for the help! > > - Gary > > On Wednesday, July 16, 2014 2:37:14 PM UTC-4, [email protected] 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! >> >> - Gary >> > -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
