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 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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