David ‹ This morning I soldered the 4.7k resistors to the pins and I see no change in operation under MSDOS. I did run the RAM test within the monitor for 10 loops with no problems. Maybe I¹ll leave it running for a few hours and see how far it gets.
Rich -- Rich Cini Collector of Classic Computers Build Master and lead engineer, Altair32 Emulator http://www.classiccmp.org/cini http://www.classiccmp.org/altair32 From: David Fry <[email protected]> Reply-To: S100-Post <[email protected]> Date: Saturday, April 18, 2015 at 1:54 PM To: S100-Post <[email protected]> Subject: Re: [N8VEM-S100:6766] Re: S100 8088 CPU Board Crashing/Unstable Hi Rich, you say 'the system is stable without the pull-ups' Do you mean it is stable when the 8088 has control of the bus ? did you solve your original problem with the 8088 then ? regards & thanks David Fry On Saturday, April 18, 2015 at 6:34:40 PM UTC+1, AltairManRich wrote: > Thanks David. As of now, the system is stable without the pull-ups, but I > haven't used it in a while. I'll run it tonight and see if I have any issues > with MEM. I'll also look at which chips I'm using. My system is fully loaded. > > Sent from my iPhone > > On Apr 18, 2015, at 1:17 PM, David Fry <[email protected] <javascript:> > > wrote: > >> Hi folks, >> >> A quick update on progress made. >> >> The new bus controller IC (D8288) arrived this morning, a ceramic Intel part >> and not the ceramic AMD part I ordered but I'll let that one go. >> >> Fitting the Intel bus controller brought an immediate improvement to the >> situation but not a 100% cure, the CPU card still intermittently locks up but >> FAR less than it did. I tried the NEC V20 CPU I have and that now also seems >> to work and I can get into MSDOS and copy files from one folder to another, >> something I previously couldn't do. >> >> I still have the Intel CPU on order and will give that a try when it arrives >> but in the meantime I dug out my IBM Technical Reference Manual for the PC-XT >> to see how IBM implemented the D8288. What immediately jumped out at me was >> that on the Memory & I/O read write lines (pins 12, 8, 13, & 7) they have >> implemented 4.7k pull up resistors, checking the D8288 data sheets from 3 >> different manufacturers revealed no mention of the need for these resistors. >> I therefore conjecture that IBM have used them to sharpen the leading edges >> of these control signals to counteract the capacitance of all the combined >> gate inputs the D8288 is driving across the motherboard (correct me if I'm >> wrong). >> >> Referring to Johns 8088 schematic I cannot see these resistors implemented >> but on the Sergey Xi8088 he seems to have used 10k pull ups on these 4 >> signals. >> So over the next few days I will add the 4.7k resistors and conduct longer >> term testing (outside of a CPU swap) to see if the pull up resistors add any >> value to the problem. >> >> Rich, if you are reading this, give the pull ups a go before swapping out the >> bus controller. >> >> Oh... and can someone else try running the MSDOS command MEM, it still hangs >> my 8088 CPU but not the 80286, would appreciate feedback on this one. >> >> best regards >> >> David Fry >> >> On Friday, April 17, 2015 at 10:36:00 PM UTC+1, David Fry wrote: >>> Hi everyone, >>> >>> I've recently plugged my 8088 CPU board into my S100 system and have been >>> having problems with the 8088 CPU board crashing/locking up. >>> My system comprises all S100Computers.com <http://S100Computers.com> boards >>> >>> Prop I/O Console V01 >>> 16MB V3 Static Ram Board >>> V2 MSDOS support board >>> V2 Z80Master CPU Board >>> V1 8088 CPU Board (Slave) >>> V1 ZFDC Floppy Controller >>> V2 S100 IDE/CF Board >>> >>> The 8088 board was inspected for damage before construction, All >>> resistors/capacitors/sil arrays are new & checked with >>> multimeter/capacitance meter before soldering to the board, >>> All TTL logic chips (TI branded) are new, all jumpers were initially set as >>> per Johns webpage and double checked and the 3 x 47pf capacitors are in the >>> correct locations. >>> >>> The symptoms are similar to what AltairManRich had been experiencing in a >>> few previous posts but no conclusion has been posted. >>> >>> Basically, I can boot my system into the Z80 monitor and transfer control to >>> the 8088 CPU which signs on with it's banner, I can press 'K' and bring up >>> the monitor menu, most monitor commands seem to work fine but menu option >>> 'J' memory test (specifying 1000,2000 as parameters) always results in the >>> 8088 CPU card going into LaLa Land >>> as Rich puts it, just filling the screen with spaces and scrolling, only a >>> hard reset recovers the system. Occasionally the 8088 CPU will go into a >>> HALT state rather than scrolling spaces. >>> >>> I can 75% of the time get the 8088 CPU card to boot MSDOS 4.01 sometimes it >>> hangs but most of the time I can get a directory listing, but copying a file >>> to a folder will cause the >>> system to freeze, also running the MSDOS command MEM always results in a >>> system lockup. >>> >>> If I drop the 8088 CPU card out of the system and place my 80286 card into >>> the system everything mentioned above works fine without an issue so the >>> fault would seem to be on the 8088 CPU board. >>> >>> Studying the jumpers and schematic I can improve matters if I jumper K5 2-3, >>> K6 2-3, K7 2-3, K11 2-3, K13 2-3 which obviously is tweaking the bus signal >>> timing to come more from >>> U68 the bus controller IC, the monitor memory test 'J' then seems to work >>> fine but the system is still not totally stable under DOS and I can get it >>> to crash. Lowering the CPU speed to 4.77Mhz makes no difference the fault >>> remains. >>> >>> My CPU is a Fujitsu MBL8088-1 and the bus controller IC is a UMC82C88, both >>> of these IC's were supplied as 'NOS' but I can't remember the vendor now. >>> I also have a NEC V20 CPU I have just had delivered from UTsource, if I fit >>> this IC then the system stability is much worse >>> >>> >>> So I have now ordered a 'NEW' Intel 8088-2 and a 'NEW' AMD8288 (non-cmos) >>> bus controller to see if that changes the situation. >>> >>> Are there any other recent 8088 CPU board builders having problems with this >>> board ? >>> Rich, did you fix your board ? >>> >>> regards >>> >>> David Fry >>> >>> >> >> -- >> 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] <javascript:> . >> For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. 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