RE: [N8VEM-S100:4686] MSDOS Support V2 PCB RTC problem.

There are two main possibilities Gary with that (excellent) setup.

Either the clock chip or crystal is bad, try another from a different vender

Or some other chip on the board is interfering with the onboard bidirectional data bus.

I’m assuming of course you have the reset jumper p52 not connected (no jumper).

I’m assuming all solder joints are good and no bridges.

For the second option, remove the 8254, 8259A and keyboard controller. Try again the add back one a t a time.

Let’s see what happens.

John

From: geka...@gmail.com [mailto:geka...@gmail.com]
Sent: Thursday, July 24, 2014 10:40 AM
To: n8vem...@googlegroups.com
Cc: mon...@vitasoft.org
Subject: Re: [N8VEM-S100:4686] MSDOS Support V2 PCB RTC problem.

Sorry, here's a better description of the system.

Compupro motherboard with switching power supplies (7.5v adjusted upwards to 8v). The BUSS is actively terminated with the Compupro circuit.

All N8VEM-S100 boards at default port settings:

Z80 CPU V2 with V5.02 monitor. Both 4 and 6mhz tried, as well as 0-4 wait states.
8088 Master Slave CPU card. Both 4.77 and 8mhz tried, as well as 0 - 4 wait states. V10.32 monitor
4mb SRAM
System Monitor Board V2
Parallel Ports I/O Board.
Propeller Console I/O Board.
Serial I/O board with Speech Chip and USB ports.
Dual IDE Board with CP/M 3.0 - "Yoda" bios

I've also tried a more minimal system with only the Z80/8088/4mb/SMB/Console I/O boards.

The clock chip has never worked. I can access registers using CP/M Based Z-RTC program. The clock never advances (eg if I set it at 01:20/20 it will always read that time).

I have changed DS12885, XTAL, Battery, 74LS32 and 74LS02 in the address decoding. I can see pulses on DS12885 pin's 14 and 17 with accessing.

Thanks for any suggestions!

- Gary

On Thursday, July 24, 2014 11:56:33 AM UTC-4, monahanz wrote:

Gary need more information to offer any help. It’s almost impossible to guess at the problem with questions like this without very detailed information.

For you, and other users when problems arise, please provide:-

A detailed makeup of your system. Boards in the system, ideally, ports used.

Speed of the CPU, wait states used.

Monitor(s) version(s).

Type of S100 motherboard.

CPM/MSDOS versions being used

Source of BIOS(s)

History, what works, did the problem suddenly appear or it never worked.

Specifically in this case, “doesn’t change over time” . What does that mean. When you read all the registers with the diagnostic program over time, what values do you get when you dump the clock’s RAM.

Same values a minute later?

Are you sure no other board is using ports 70 & 71H.

Try a second DS chip. If you still have problems I will take a look at it for you

John

From: n8ve...@googlegroups.com [mailto:n8ve...@googlegroups.com] On Behalf Of gek...@gmail.com
Sent: Thursday, July 24, 2014 7:31 AM
To: n8ve...@googlegroups.com
Cc: mon...@vitasoft.org
Subject: Re: [N8VEM-S100:4686] MSDOS Support V2 PCB RTC problem.

I continue to have no luck with the RTC. Strange symptoms...

I can set the clock with the CP/M Z-RTC program, but it doesn't change over time.

I can set the clock with the 8088 monitor V10.32 "E" command and only the seconds and day portions will change.

I've swapped out the battery, xtal, DS12885+, and support IC's.

I've ordered a DS12887 to try, as that should eliminate the xtal and battery as issues.

The rest of the board (Eprom access, Interrupt controller, Timer) work fine. I still haven't tested the Keyboard controller section.

I'm almost ready to just build up a second board. Any ideas or suggested troubleshooting procedures?

- Gary

On Thursday, July 17, 2014 10:03:16 AM UTC-4, gek...@gmail.com wrote:

John -

Crystal should be here in a few days, finger's crossed.

I'll also try simplifying the system tonight and using the Z-RTC program under CP/M3 instead of the 8088 board. I'll see if that makes any difference.

- Gary

On Thursday, July 17, 2014 12:36:10 AM UTC-4, monahanz wrote:

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:n8ve...@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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