Unfortunately I have no idea of the specs for the xtal that ultimately worked.
I didn't pay much attention to the specs when selecting at 32.768 crystal - and hadn't seen the application note that Frank referenced (very helpful). If anyone has used a specific part that worked it would be helpful to post a part number for the group. - Gary On Friday, July 25, 2014 8:41:01 AM UTC-4, David Fry wrote: > > 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.
